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([2620:10d:c090:500::5:2f5b]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-201f0395b9bsm82237135ad.237.2024.08.20.15.06.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Aug 2024 15:06:08 -0700 (PDT) Message-ID: <48359591-314d-42b0-8332-58f9f6041330@davidwei.uk> Date: Tue, 20 Aug 2024 15:06:06 -0700 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] io_uring: implement our own schedule timeout handling Content-Language: en-GB To: Jens Axboe , io-uring@vger.kernel.org References: <20240819233042.230956-1-axboe@kernel.dk> <20240819233042.230956-4-axboe@kernel.dk> <58a42e82-3742-4439-998e-c9389c5849bc@davidwei.uk> From: David Wei In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2024-08-20 14:39, Jens Axboe wrote: > On 8/20/24 3:37 PM, David Wei wrote: >> On 2024-08-20 14:34, Jens Axboe wrote: >>> On 8/20/24 2:08 PM, David Wei wrote: >>>> On 2024-08-19 16:28, Jens Axboe wrote: >>>>> In preparation for having two distinct timeouts and avoid waking the >>>>> task if we don't need to. >>>>> >>>>> Signed-off-by: Jens Axboe >>>>> --- >>>>> io_uring/io_uring.c | 41 ++++++++++++++++++++++++++++++++++++----- >>>>> io_uring/io_uring.h | 2 ++ >>>>> 2 files changed, 38 insertions(+), 5 deletions(-) >>>>> >>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c >>>>> index 9e2b8d4c05db..ddfbe04c61ed 100644 >>>>> --- a/io_uring/io_uring.c >>>>> +++ b/io_uring/io_uring.c >>>>> @@ -2322,7 +2322,7 @@ static int io_wake_function(struct wait_queue_entry *curr, unsigned int mode, >>>>> * Cannot safely flush overflowed CQEs from here, ensure we wake up >>>>> * the task, and the next invocation will do it. >>>>> */ >>>>> - if (io_should_wake(iowq) || io_has_work(iowq->ctx)) >>>>> + if (io_should_wake(iowq) || io_has_work(iowq->ctx) || iowq->hit_timeout) >>>> >>>> iowq->hit_timeout may be modified in a timer softirq context, while this >>>> wait_queue_func_t (AIUI) may get called from any context e.g. >>>> net_rx_softirq for sockets. Does this need a READ_ONLY()? >>> >>> Yes probably not a bad idea to make it READ_ONCE(). >>> >>>>> return autoremove_wake_function(curr, mode, wake_flags, key); >>>>> return -1; >>>>> } >>>>> @@ -2350,6 +2350,38 @@ static bool current_pending_io(void) >>>>> return percpu_counter_read_positive(&tctx->inflight); >>>>> } >>>>> >>>>> +static enum hrtimer_restart io_cqring_timer_wakeup(struct hrtimer *timer) >>>>> +{ >>>>> + struct io_wait_queue *iowq = container_of(timer, struct io_wait_queue, t); >>>>> + struct io_ring_ctx *ctx = iowq->ctx; >>>>> + >>>>> + WRITE_ONCE(iowq->hit_timeout, 1); >>>>> + if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) >>>>> + wake_up_process(ctx->submitter_task); >>>>> + else >>>>> + io_cqring_wake(ctx); >>>> >>>> This is a bit different to schedule_hrtimeout_range_clock(). Why is >>>> io_cqring_wake() needed here for non-DEFER_TASKRUN? >>> >>> That's how the wakeups work - for defer taskrun, the task isn't on a >>> waitqueue at all. Hence we need to wake the task itself. For any other >>> setup, they will be on the waitqueue, and we just call io_cqring_wake() >>> to wake up anyone waiting on the waitqueue. That will iterate the wake >>> queue and call handlers for each item. Having a separate handler for >>> that will allow to NOT wake up the task if we don't need to. >>> taskrun, the waker >> >> To rephase the question, why is the original code calling >> schedule_hrtimeout_range_clock() not needing to differentiate behaviour >> between defer taskrun and not? > > Because that part is the same, the task schedules out and goes to sleep. > That has always been the same regardless of how the ring is setup. Only > difference is that DEFER_TASKRUN doesn't add itself to ctx->wait, and > hence cannot be woken by a wake_up(ctx->wait). We have to wake the task > manually. > io_cqring_timer_wakeup() is the timer expired callback which calls wake_up_process() or io_cqring_wake() depending on DEFER_TASKRUN. The original code calling schedule_hrtimeout_range_clock() uses hrtimer_sleeper instead, which has a default timer expired callback set to hrtimer_wakeup(). hrtimer_wakeup() only calls wake_up_process(). My question is: why this asymmetry? Why does the new custom callback require io_cqring_wake()?