| Message ID | 20230605212009.1992313-3-shr@devkernel.io (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | io_uring: add napi busy polling support | expand |
On Mon, Jun 05, 2023 at 02:20:03PM -0700, Stefan Roesch wrote: > This introduces the napi_busy_loop_rcu() function. If the caller of > napi_busy_loop() function is also taking the rcu read lock, it is possible > that napi_busy_loop() is releasing the read lock if it invokes schedule. > However the caller is expecting that the rcu read lock is not released > until the function completes. This new function avoids that problem. It > expects that the caller MUST hold the rcu_read_lock while calling this > function. > > Signed-off-by: Stefan Roesch <shr@devkernel.io> Hi Stefan, some minor nits from my side, which you may want to consider if you need to spin a v15 for some reason. ... > diff --git a/net/core/dev.c b/net/core/dev.c > index f4677aa20f84..fcd4a6a70646 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -6213,6 +6213,37 @@ static inline void __napi_busy_poll(struct napi_busy_poll_ctx *ctx, > LINUX_MIB_BUSYPOLLRXPACKETS, work); > local_bh_enable(); > } > + > +/* > + * Warning: can exit without calling need_resched(). > + */ For historical reasons, multi-line comments in Networking code are like this. /* Something * more */ Though I notice that dev.c doesn't follow this too closely, perhaps for other historical reasons. Anyway, in this case I'd suggest a single like comment. Unless there is something more to say. /* Warning: can exit without calling need_resched(). */ > +void napi_busy_loop_rcu(unsigned int napi_id, > + bool (*loop_end)(void *, unsigned long), > + void *loop_end_arg, bool prefer_busy_poll, u16 budget) The indentation of the above two likes should align with the inside of the opening parentheses. void napi_busy_loop_rcu(unsigned int napi_id, bool (*loop_end)(void *, unsigned long), void *loop_end_arg, bool prefer_busy_poll, u16 budget) ...
diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h index f90f0021f5f2..622623f5740e 100644 --- a/include/net/busy_poll.h +++ b/include/net/busy_poll.h @@ -47,6 +47,10 @@ void napi_busy_loop(unsigned int napi_id, bool (*loop_end)(void *, unsigned long), void *loop_end_arg, bool prefer_busy_poll, u16 budget); +void napi_busy_loop_rcu(unsigned int napi_id, + bool (*loop_end)(void *, unsigned long), + void *loop_end_arg, bool prefer_busy_poll, u16 budget); + #else /* CONFIG_NET_RX_BUSY_POLL */ static inline unsigned long net_busy_loop_on(void) { diff --git a/net/core/dev.c b/net/core/dev.c index f4677aa20f84..fcd4a6a70646 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6213,6 +6213,37 @@ static inline void __napi_busy_poll(struct napi_busy_poll_ctx *ctx, LINUX_MIB_BUSYPOLLRXPACKETS, work); local_bh_enable(); } + +/* + * Warning: can exit without calling need_resched(). + */ +void napi_busy_loop_rcu(unsigned int napi_id, + bool (*loop_end)(void *, unsigned long), + void *loop_end_arg, bool prefer_busy_poll, u16 budget) +{ + unsigned long start_time = loop_end ? busy_loop_current_time() : 0; + struct napi_busy_poll_ctx ctx = {}; + + ctx.napi = napi_by_id(napi_id); + if (!ctx.napi) + return; + + preempt_disable(); + for (;;) { + __napi_busy_poll(&ctx, prefer_busy_poll, budget); + + if (!loop_end || loop_end(loop_end_arg, start_time)) + break; + if (unlikely(need_resched())) + break; + + cpu_relax(); + } + if (ctx.napi_poll) + busy_poll_stop(ctx.napi, ctx.have_poll_lock, prefer_busy_poll, budget); + preempt_enable(); +} + void napi_busy_loop(unsigned int napi_id, bool (*loop_end)(void *, unsigned long), void *loop_end_arg, bool prefer_busy_poll, u16 budget)
This introduces the napi_busy_loop_rcu() function. If the caller of napi_busy_loop() function is also taking the rcu read lock, it is possible that napi_busy_loop() is releasing the read lock if it invokes schedule. However the caller is expecting that the rcu read lock is not released until the function completes. This new function avoids that problem. It expects that the caller MUST hold the rcu_read_lock while calling this function. Signed-off-by: Stefan Roesch <shr@devkernel.io> --- include/net/busy_poll.h | 4 ++++ net/core/dev.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+)