| Message ID | 20210601055728.90849-3-slp@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | nbd/server: Quiesce server on drained section | expand |
Am 01.06.2021 um 07:57 hat Sergio Lopez geschrieben: > Before switching between AioContexts we need to make sure that we're > fully quiesced ("nb_requests == 0" for every client) when entering the > drained section. > > To do this, we set "quiescing = true" for every client on > ".drained_begin" to prevent new coroutines to be created, and check if > "nb_requests == 0" on ".drained_poll". Finally, once we're exiting the > drained section, on ".drained_end" we set "quiescing = false" and > call "nbd_client_receive_next_request()" to resume the processing of > new requests. > > With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be > reverted to be as simple as they were before f148ae7d36. > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1960137 > Suggested-by: Kevin Wolf <kwolf@redhat.com> > Signed-off-by: Sergio Lopez <slp@redhat.com> > --- > nbd/server.c | 99 +++++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 75 insertions(+), 24 deletions(-) > > diff --git a/nbd/server.c b/nbd/server.c > index 86a44a9b41..33e55479d7 100644 > --- a/nbd/server.c > +++ b/nbd/server.c > @@ -132,7 +132,7 @@ struct NBDClient { > CoMutex send_lock; > Coroutine *send_coroutine; > > - bool read_yielding; > + GSList *yield_co_list; /* List of coroutines yielding on nbd_read_eof */ > bool quiescing; Hm, how do you get more than one coroutine per client yielding in nbd_read_eof() at the same time? I thought the model is that you always have one coroutine reading the next request (which is client->recv_coroutine) and all the others are just processing the request they had read earlier. Multiple coroutines reading from the same socket would sound like a bad idea. > QTAILQ_ENTRY(NBDClient) next; > @@ -1367,6 +1367,7 @@ static inline int coroutine_fn > nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) > { > bool partial = false; > + Coroutine *co; > > assert(size); > while (size > 0) { > @@ -1375,9 +1376,12 @@ nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) > > len = qio_channel_readv(client->ioc, &iov, 1, errp); > if (len == QIO_CHANNEL_ERR_BLOCK) { > - client->read_yielding = true; > + co = qemu_coroutine_self(); > + > + client->yield_co_list = g_slist_prepend(client->yield_co_list, co); > qio_channel_yield(client->ioc, G_IO_IN); > - client->read_yielding = false; > + client->yield_co_list = g_slist_remove(client->yield_co_list, co); > + > if (client->quiescing) { > return -EAGAIN; > } > @@ -1513,6 +1517,11 @@ static void nbd_request_put(NBDRequestData *req) > g_free(req); > > client->nb_requests--; > + > + if (client->quiescing && client->nb_requests == 0) { > + aio_wait_kick(); > + } > + > nbd_client_receive_next_request(client); > > nbd_client_put(client); > @@ -1530,49 +1539,75 @@ static void blk_aio_attached(AioContext *ctx, void *opaque) > QTAILQ_FOREACH(client, &exp->clients, next) { > qio_channel_attach_aio_context(client->ioc, ctx); > > + assert(client->nb_requests == 0); > assert(client->recv_coroutine == NULL); > assert(client->send_coroutine == NULL); > - > - if (client->quiescing) { > - client->quiescing = false; > - nbd_client_receive_next_request(client); > - } > } > } > > -static void nbd_aio_detach_bh(void *opaque) > +static void blk_aio_detach(void *opaque) > { > NBDExport *exp = opaque; > NBDClient *client; > > + trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); > + > QTAILQ_FOREACH(client, &exp->clients, next) { > qio_channel_detach_aio_context(client->ioc); > + } > + > + exp->common.ctx = NULL; > +} > + > +static void nbd_drained_begin(void *opaque) > +{ > + NBDExport *exp = opaque; > + NBDClient *client; > + > + QTAILQ_FOREACH(client, &exp->clients, next) { > client->quiescing = true; > + } > +} > > - if (client->recv_coroutine) { > - if (client->read_yielding) { > - qemu_aio_coroutine_enter(exp->common.ctx, > - client->recv_coroutine); > - } else { > - AIO_WAIT_WHILE(exp->common.ctx, client->recv_coroutine != NULL); > - } > - } > +static void nbd_drained_end(void *opaque) > +{ > + NBDExport *exp = opaque; > + NBDClient *client; > > - if (client->send_coroutine) { > - AIO_WAIT_WHILE(exp->common.ctx, client->send_coroutine != NULL); > - } > + QTAILQ_FOREACH(client, &exp->clients, next) { > + client->quiescing = false; > + nbd_client_receive_next_request(client); > } > } > > -static void blk_aio_detach(void *opaque) > +static bool nbd_drained_poll(void *opaque) > { > NBDExport *exp = opaque; > + NBDClient *client; > + Coroutine *co; > + GSList *entry; > + GSList *coroutine_list; > > - trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); > + QTAILQ_FOREACH(client, &exp->clients, next) { > + if (client->nb_requests != 0) { > + /* > + * Enter coroutines waiting for new requests on nbd_read_eof(), so > + * we don't depend on the client to wake us up. > + */ > + coroutine_list = g_slist_copy(client->yield_co_list); > + for (entry = coroutine_list; > + entry != NULL; > + entry = g_slist_next(entry)) { > + co = entry->data; > + qemu_aio_coroutine_enter(exp->common.ctx, co); > + } > + g_slist_free(coroutine_list); > > - aio_wait_bh_oneshot(exp->common.ctx, nbd_aio_detach_bh, exp); > + return 1; This would be more accurately spelt true... > + } > + } > > - exp->common.ctx = NULL; > + return 0; ...and this false. > } > > static void nbd_eject_notifier(Notifier *n, void *data) The patch looks correct to me, though I'm not sure if yield_co_list is an unnecessary complication (and if it isn't, whether that's safe). I would be happy enough to apply it anyway if you can explain the yield_co_list thing, but I'll give Eric some time to have a look, too. Kevin
On Tue, Jun 01, 2021 at 06:08:41PM +0200, Kevin Wolf wrote: > Am 01.06.2021 um 07:57 hat Sergio Lopez geschrieben: > > Before switching between AioContexts we need to make sure that we're > > fully quiesced ("nb_requests == 0" for every client) when entering the > > drained section. > > > > To do this, we set "quiescing = true" for every client on > > ".drained_begin" to prevent new coroutines to be created, and check if > > "nb_requests == 0" on ".drained_poll". Finally, once we're exiting the > > drained section, on ".drained_end" we set "quiescing = false" and > > call "nbd_client_receive_next_request()" to resume the processing of > > new requests. > > > > With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be > > reverted to be as simple as they were before f148ae7d36. > > > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1960137 > > Suggested-by: Kevin Wolf <kwolf@redhat.com> > > Signed-off-by: Sergio Lopez <slp@redhat.com> > > --- > > nbd/server.c | 99 +++++++++++++++++++++++++++++++++++++++------------- > > 1 file changed, 75 insertions(+), 24 deletions(-) > > > > diff --git a/nbd/server.c b/nbd/server.c > > index 86a44a9b41..33e55479d7 100644 > > --- a/nbd/server.c > > +++ b/nbd/server.c > > @@ -132,7 +132,7 @@ struct NBDClient { > > CoMutex send_lock; > > Coroutine *send_coroutine; > > > > - bool read_yielding; > > + GSList *yield_co_list; /* List of coroutines yielding on nbd_read_eof */ > > bool quiescing; > > Hm, how do you get more than one coroutine per client yielding in > nbd_read_eof() at the same time? I thought the model is that you always > have one coroutine reading the next request (which is > client->recv_coroutine) and all the others are just processing the > request they had read earlier. Multiple coroutines reading from the > same socket would sound like a bad idea. You're right, there's only a single coroutine yielding on nbd_read_eof(). I've added the list while at a moment I was trying to keep track of every coroutine, and I kept it without thinking if it was really needed. I'll drop it, entering just client->recv_coroutine is it isn't NULL. > > QTAILQ_ENTRY(NBDClient) next; > > @@ -1367,6 +1367,7 @@ static inline int coroutine_fn > > nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) > > { > > bool partial = false; > > + Coroutine *co; > > > > assert(size); > > while (size > 0) { > > @@ -1375,9 +1376,12 @@ nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) > > > > len = qio_channel_readv(client->ioc, &iov, 1, errp); > > if (len == QIO_CHANNEL_ERR_BLOCK) { > > - client->read_yielding = true; > > + co = qemu_coroutine_self(); > > + > > + client->yield_co_list = g_slist_prepend(client->yield_co_list, co); > > qio_channel_yield(client->ioc, G_IO_IN); > > - client->read_yielding = false; > > + client->yield_co_list = g_slist_remove(client->yield_co_list, co); > > + > > if (client->quiescing) { > > return -EAGAIN; > > } > > @@ -1513,6 +1517,11 @@ static void nbd_request_put(NBDRequestData *req) > > g_free(req); > > > > client->nb_requests--; > > + > > + if (client->quiescing && client->nb_requests == 0) { > > + aio_wait_kick(); > > + } > > + > > nbd_client_receive_next_request(client); > > > > nbd_client_put(client); > > @@ -1530,49 +1539,75 @@ static void blk_aio_attached(AioContext *ctx, void *opaque) > > QTAILQ_FOREACH(client, &exp->clients, next) { > > qio_channel_attach_aio_context(client->ioc, ctx); > > > > + assert(client->nb_requests == 0); > > assert(client->recv_coroutine == NULL); > > assert(client->send_coroutine == NULL); > > - > > - if (client->quiescing) { > > - client->quiescing = false; > > - nbd_client_receive_next_request(client); > > - } > > } > > } > > > > -static void nbd_aio_detach_bh(void *opaque) > > +static void blk_aio_detach(void *opaque) > > { > > NBDExport *exp = opaque; > > NBDClient *client; > > > > + trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); > > + > > QTAILQ_FOREACH(client, &exp->clients, next) { > > qio_channel_detach_aio_context(client->ioc); > > + } > > + > > + exp->common.ctx = NULL; > > +} > > + > > +static void nbd_drained_begin(void *opaque) > > +{ > > + NBDExport *exp = opaque; > > + NBDClient *client; > > + > > + QTAILQ_FOREACH(client, &exp->clients, next) { > > client->quiescing = true; > > + } > > +} > > > > - if (client->recv_coroutine) { > > - if (client->read_yielding) { > > - qemu_aio_coroutine_enter(exp->common.ctx, > > - client->recv_coroutine); > > - } else { > > - AIO_WAIT_WHILE(exp->common.ctx, client->recv_coroutine != NULL); > > - } > > - } > > +static void nbd_drained_end(void *opaque) > > +{ > > + NBDExport *exp = opaque; > > + NBDClient *client; > > > > - if (client->send_coroutine) { > > - AIO_WAIT_WHILE(exp->common.ctx, client->send_coroutine != NULL); > > - } > > + QTAILQ_FOREACH(client, &exp->clients, next) { > > + client->quiescing = false; > > + nbd_client_receive_next_request(client); > > } > > } > > > > -static void blk_aio_detach(void *opaque) > > +static bool nbd_drained_poll(void *opaque) > > { > > NBDExport *exp = opaque; > > + NBDClient *client; > > + Coroutine *co; > > + GSList *entry; > > + GSList *coroutine_list; > > > > - trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); > > + QTAILQ_FOREACH(client, &exp->clients, next) { > > + if (client->nb_requests != 0) { > > + /* > > + * Enter coroutines waiting for new requests on nbd_read_eof(), so > > + * we don't depend on the client to wake us up. > > + */ > > + coroutine_list = g_slist_copy(client->yield_co_list); > > + for (entry = coroutine_list; > > + entry != NULL; > > + entry = g_slist_next(entry)) { > > + co = entry->data; > > + qemu_aio_coroutine_enter(exp->common.ctx, co); > > + } > > + g_slist_free(coroutine_list); > > > > - aio_wait_bh_oneshot(exp->common.ctx, nbd_aio_detach_bh, exp); > > + return 1; > > This would be more accurately spelt true... > > > + } > > + } > > > > - exp->common.ctx = NULL; > > + return 0; > > ...and this false. I'll change this in v2. Thanks, Sergio. > > } > > > > static void nbd_eject_notifier(Notifier *n, void *data) > > The patch looks correct to me, though I'm not sure if yield_co_list is > an unnecessary complication (and if it isn't, whether that's safe). > > I would be happy enough to apply it anyway if you can explain the > yield_co_list thing, but I'll give Eric some time to have a look, too. > > Kevin >
On Tue, Jun 01, 2021 at 07:57:28AM +0200, Sergio Lopez wrote: > Before switching between AioContexts we need to make sure that we're > fully quiesced ("nb_requests == 0" for every client) when entering the > drained section. > > To do this, we set "quiescing = true" for every client on > ".drained_begin" to prevent new coroutines to be created, and check if s/to be created/from being created/ > "nb_requests == 0" on ".drained_poll". Finally, once we're exiting the > drained section, on ".drained_end" we set "quiescing = false" and > call "nbd_client_receive_next_request()" to resume the processing of > new requests. > > With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be > reverted to be as simple as they were before f148ae7d36. Is that reversion planned to be patch 3 of your series in v2? > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1960137 > Suggested-by: Kevin Wolf <kwolf@redhat.com> > Signed-off-by: Sergio Lopez <slp@redhat.com> > --- > nbd/server.c | 99 +++++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 75 insertions(+), 24 deletions(-) >
On Tue, Jun 01, 2021 at 06:31:29PM +0200, Sergio Lopez wrote: > > Hm, how do you get more than one coroutine per client yielding in > > nbd_read_eof() at the same time? I thought the model is that you always > > have one coroutine reading the next request (which is > > client->recv_coroutine) and all the others are just processing the > > request they had read earlier. Multiple coroutines reading from the > > same socket would sound like a bad idea. > > You're right, there's only a single coroutine yielding on > nbd_read_eof(). I've added the list while at a moment I was trying to > keep track of every coroutine, and I kept it without thinking if it > was really needed. > > I'll drop it, entering just client->recv_coroutine is it isn't NULL. Sounds like I'll wait for the v2 before applying. But the overall logic changes made sense to me. > > The patch looks correct to me, though I'm not sure if yield_co_list is > > an unnecessary complication (and if it isn't, whether that's safe). > > > > I would be happy enough to apply it anyway if you can explain the > > yield_co_list thing, but I'll give Eric some time to have a look, too. Thanks for catching my attention on this!
On Tue, Jun 01, 2021 at 04:29:07PM -0500, Eric Blake wrote: > On Tue, Jun 01, 2021 at 07:57:28AM +0200, Sergio Lopez wrote: > > Before switching between AioContexts we need to make sure that we're > > fully quiesced ("nb_requests == 0" for every client) when entering the > > drained section. > > > > To do this, we set "quiescing = true" for every client on > > ".drained_begin" to prevent new coroutines to be created, and check if > > s/to be created/from being created/ > > > "nb_requests == 0" on ".drained_poll". Finally, once we're exiting the > > drained section, on ".drained_end" we set "quiescing = false" and > > call "nbd_client_receive_next_request()" to resume the processing of > > new requests. > > > > With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be > > reverted to be as simple as they were before f148ae7d36. > > Is that reversion planned to be patch 3 of your series in v2? Actually, we need part of the changes introduced in f148ae7d36, so it's probably simpler to manually revert "blk_aio_attach()" and "blk_aio_detach()" here than doing an actual reversion and then reintroducing the changes. Thanks, Sergio.
diff --git a/nbd/server.c b/nbd/server.c index 86a44a9b41..33e55479d7 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -132,7 +132,7 @@ struct NBDClient { CoMutex send_lock; Coroutine *send_coroutine; - bool read_yielding; + GSList *yield_co_list; /* List of coroutines yielding on nbd_read_eof */ bool quiescing; QTAILQ_ENTRY(NBDClient) next; @@ -1367,6 +1367,7 @@ static inline int coroutine_fn nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) { bool partial = false; + Coroutine *co; assert(size); while (size > 0) { @@ -1375,9 +1376,12 @@ nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) len = qio_channel_readv(client->ioc, &iov, 1, errp); if (len == QIO_CHANNEL_ERR_BLOCK) { - client->read_yielding = true; + co = qemu_coroutine_self(); + + client->yield_co_list = g_slist_prepend(client->yield_co_list, co); qio_channel_yield(client->ioc, G_IO_IN); - client->read_yielding = false; + client->yield_co_list = g_slist_remove(client->yield_co_list, co); + if (client->quiescing) { return -EAGAIN; } @@ -1513,6 +1517,11 @@ static void nbd_request_put(NBDRequestData *req) g_free(req); client->nb_requests--; + + if (client->quiescing && client->nb_requests == 0) { + aio_wait_kick(); + } + nbd_client_receive_next_request(client); nbd_client_put(client); @@ -1530,49 +1539,75 @@ static void blk_aio_attached(AioContext *ctx, void *opaque) QTAILQ_FOREACH(client, &exp->clients, next) { qio_channel_attach_aio_context(client->ioc, ctx); + assert(client->nb_requests == 0); assert(client->recv_coroutine == NULL); assert(client->send_coroutine == NULL); - - if (client->quiescing) { - client->quiescing = false; - nbd_client_receive_next_request(client); - } } } -static void nbd_aio_detach_bh(void *opaque) +static void blk_aio_detach(void *opaque) { NBDExport *exp = opaque; NBDClient *client; + trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); + QTAILQ_FOREACH(client, &exp->clients, next) { qio_channel_detach_aio_context(client->ioc); + } + + exp->common.ctx = NULL; +} + +static void nbd_drained_begin(void *opaque) +{ + NBDExport *exp = opaque; + NBDClient *client; + + QTAILQ_FOREACH(client, &exp->clients, next) { client->quiescing = true; + } +} - if (client->recv_coroutine) { - if (client->read_yielding) { - qemu_aio_coroutine_enter(exp->common.ctx, - client->recv_coroutine); - } else { - AIO_WAIT_WHILE(exp->common.ctx, client->recv_coroutine != NULL); - } - } +static void nbd_drained_end(void *opaque) +{ + NBDExport *exp = opaque; + NBDClient *client; - if (client->send_coroutine) { - AIO_WAIT_WHILE(exp->common.ctx, client->send_coroutine != NULL); - } + QTAILQ_FOREACH(client, &exp->clients, next) { + client->quiescing = false; + nbd_client_receive_next_request(client); } } -static void blk_aio_detach(void *opaque) +static bool nbd_drained_poll(void *opaque) { NBDExport *exp = opaque; + NBDClient *client; + Coroutine *co; + GSList *entry; + GSList *coroutine_list; - trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); + QTAILQ_FOREACH(client, &exp->clients, next) { + if (client->nb_requests != 0) { + /* + * Enter coroutines waiting for new requests on nbd_read_eof(), so + * we don't depend on the client to wake us up. + */ + coroutine_list = g_slist_copy(client->yield_co_list); + for (entry = coroutine_list; + entry != NULL; + entry = g_slist_next(entry)) { + co = entry->data; + qemu_aio_coroutine_enter(exp->common.ctx, co); + } + g_slist_free(coroutine_list); - aio_wait_bh_oneshot(exp->common.ctx, nbd_aio_detach_bh, exp); + return 1; + } + } - exp->common.ctx = NULL; + return 0; } static void nbd_eject_notifier(Notifier *n, void *data) @@ -1594,6 +1629,12 @@ void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk) blk_add_remove_bs_notifier(blk, &nbd_exp->eject_notifier); } +static const BlockDevOps nbd_block_ops = { + .drained_begin = nbd_drained_begin, + .drained_end = nbd_drained_end, + .drained_poll = nbd_drained_poll, +}; + static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args, Error **errp) { @@ -1715,8 +1756,17 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args, exp->allocation_depth = arg->allocation_depth; + /* + * We need to inhibit request queuing in the block layer to ensure we can + * be properly quiesced when entering a drained section, as our coroutines + * servicing pending requests might enter blk_pread(). + */ + blk_set_disable_request_queuing(blk, true); + blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp); + blk_set_dev_ops(blk, &nbd_block_ops, exp); + QTAILQ_INSERT_TAIL(&exports, exp, next); return 0; @@ -1788,6 +1838,7 @@ static void nbd_export_delete(BlockExport *blk_exp) } blk_remove_aio_context_notifier(exp->common.blk, blk_aio_attached, blk_aio_detach, exp); + blk_set_disable_request_queuing(exp->common.blk, false); } for (i = 0; i < exp->nr_export_bitmaps; i++) {
Before switching between AioContexts we need to make sure that we're fully quiesced ("nb_requests == 0" for every client) when entering the drained section. To do this, we set "quiescing = true" for every client on ".drained_begin" to prevent new coroutines to be created, and check if "nb_requests == 0" on ".drained_poll". Finally, once we're exiting the drained section, on ".drained_end" we set "quiescing = false" and call "nbd_client_receive_next_request()" to resume the processing of new requests. With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be reverted to be as simple as they were before f148ae7d36. RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1960137 Suggested-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Sergio Lopez <slp@redhat.com> --- nbd/server.c | 99 +++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 75 insertions(+), 24 deletions(-)