| Message ID | 1493389911-19512-5-git-send-email-axboe@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Apr 28, 2017 at 08:31:49AM -0600, Jens Axboe wrote: > Instead of bypassing the scheduler for insertion of reserved requests, > we ensure that the request is marked as RQF_RESERVED so they driver > knows where it came from. > > Usually we just use the tag to know if it's reserved or not, > but that only works when the request has a driver tag assigned. > Using RQF_RESERVED can be done independently of whether or not > scheduling is used. Do we really need a flag for this? If anyone cares if a request is internal it can just check ->tag / ->internal_tag is smaller than ->nr_reserved_tags using a little helper. I'd really like to keep the number of flags down as much as possible.
On 04/28/2017 08:41 AM, Christoph Hellwig wrote: > On Fri, Apr 28, 2017 at 08:31:49AM -0600, Jens Axboe wrote: >> Instead of bypassing the scheduler for insertion of reserved requests, >> we ensure that the request is marked as RQF_RESERVED so they driver >> knows where it came from. >> >> Usually we just use the tag to know if it's reserved or not, >> but that only works when the request has a driver tag assigned. >> Using RQF_RESERVED can be done independently of whether or not >> scheduling is used. > > Do we really need a flag for this? If anyone cares if a request > is internal it can just check ->tag / ->internal_tag is smaller > than ->nr_reserved_tags using a little helper. > > I'd really like to keep the number of flags down as much as possible. Ming had the same comment. Once we enter ->queue_rq() and later we don't need the flag, since ->tag has been assigned and the regular helper works fine. We can kill it. I forgot about this in the previous reply, but it was meant to pass the fact that this was a reserved request to get_driver_tag(), but it doesn't need that, since we already use the regular helper against ->internal_tag. I'll drop this patch.
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 8b361e192e8a..27c67465f856 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -82,11 +82,7 @@ struct request *blk_mq_sched_get_request(struct request_queue *q, if (likely(!data->hctx)) data->hctx = blk_mq_map_queue(q, data->ctx->cpu); - /* - * For a reserved tag, allocate a normal request since we might - * have driver dependencies on the value of the internal tag. - */ - if (e && !(data->flags & BLK_MQ_REQ_RESERVED)) { + if (e) { data->flags |= BLK_MQ_REQ_INTERNAL; /* @@ -104,6 +100,8 @@ struct request *blk_mq_sched_get_request(struct request_queue *q, } if (rq) { + if (data->flags & BLK_MQ_REQ_RESERVED) + rq->rq_flags |= RQF_RESERVED; if (!op_is_flush(op)) { rq->elv.icq = NULL; if (e && e->type->icq_cache) diff --git a/block/blk-mq.c b/block/blk-mq.c index b75ef2392db7..0168b27469cb 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -268,6 +268,9 @@ struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data, data->hctx->tags->rqs[rq->tag] = rq; } + if (data->flags & BLK_MQ_REQ_RESERVED) + rq->rq_flags |= RQF_RESERVED; + blk_mq_rq_ctx_init(data->q, data->ctx, rq, op); return rq; } diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index ba3884f26288..c246de5861dc 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -120,6 +120,8 @@ typedef __u32 __bitwise req_flags_t; /* Look at ->special_vec for the actual data payload instead of the bio chain. */ #define RQF_SPECIAL_PAYLOAD ((__force req_flags_t)(1 << 18)) +/* Request came from the reserved tags/pool */ +#define RQF_RESERVED ((__force req_flags_t)(1 << 19)) /* flags that prevent us from merging requests: */ #define RQF_NOMERGE_FLAGS \
Instead of bypassing the scheduler for insertion of reserved requests, we ensure that the request is marked as RQF_RESERVED so they driver knows where it came from. Usually we just use the tag to know if it's reserved or not, but that only works when the request has a driver tag assigned. Using RQF_RESERVED can be done independently of whether or not scheduling is used. Signed-off-by: Jens Axboe <axboe@fb.com> --- block/blk-mq-sched.c | 8 +++----- block/blk-mq.c | 3 +++ include/linux/blkdev.h | 2 ++ 3 files changed, 8 insertions(+), 5 deletions(-)