From: Max Kellermann <[email protected]>
To: Pavel Begunkov <[email protected]>
Cc: [email protected], [email protected], [email protected]
Subject: Re: [PATCH 4/8] io_uring/io-wq: cache work->flags in variable
Date: Wed, 29 Jan 2025 20:11:17 +0100 [thread overview]
Message-ID: <CAKPOu+-Mfx9q79nin7tGi1Rr4qGGY=y-2OhuP80U=7EtRpfBdg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
On Wed, Jan 29, 2025 at 7:56 PM Pavel Begunkov <[email protected]> wrote:
> What architecture are you running? I don't get why the reads
> are expensive while it's relaxed and there shouldn't even be
> any contention. It doesn't even need to be atomics, we still
> should be able to convert int back to plain ints.
I measured on an AMD Epyc 9654P.
As you see in my numbers, around 40% of the CPU time was wasted on
spinlock contention. Dozens of io-wq threads are trampling on each
other's feet all the time.
I don't think this is about memory accesses being exceptionally
expensive; it's just about wringing every cycle from the code section
that's under the heavy-contention spinlock.
next prev parent reply other threads:[~2025-01-29 19:11 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-28 13:39 [PATCH 0/8] Various io_uring micro-optimizations (reducing lock contention) Max Kellermann
2025-01-28 13:39 ` [PATCH 1/8] io_uring/io-wq: eliminate redundant io_work_get_acct() calls Max Kellermann
2025-01-28 13:39 ` [PATCH 2/8] io_uring/io-wq: add io_worker.acct pointer Max Kellermann
2025-01-28 13:39 ` [PATCH 3/8] io_uring/io-wq: move worker lists to struct io_wq_acct Max Kellermann
2025-01-28 13:39 ` [PATCH 4/8] io_uring/io-wq: cache work->flags in variable Max Kellermann
2025-01-29 18:57 ` Pavel Begunkov
2025-01-29 19:11 ` Max Kellermann [this message]
2025-01-29 23:41 ` Pavel Begunkov
2025-01-30 5:36 ` Max Kellermann
2025-01-30 14:57 ` Jens Axboe
2025-01-31 14:06 ` Pavel Begunkov
2025-01-30 14:54 ` Jens Axboe
2025-01-28 13:39 ` [PATCH 5/8] io_uring/io-wq: do not use bogus hash value Max Kellermann
2025-01-28 13:39 ` [PATCH 6/8] io_uring/io-wq: pass io_wq to io_get_next_work() Max Kellermann
2025-01-28 13:39 ` [PATCH 7/8] io_uring: cache io_kiocb->flags in variable Max Kellermann
2025-01-29 19:11 ` Pavel Begunkov
2025-01-28 13:39 ` [PATCH 8/8] io_uring: skip redundant poll wakeups Max Kellermann
2025-01-31 13:54 ` Pavel Begunkov
2025-01-31 17:16 ` Max Kellermann
2025-01-31 17:25 ` Pavel Begunkov
2025-01-29 17:18 ` [PATCH 0/8] Various io_uring micro-optimizations (reducing lock contention) Jens Axboe
2025-01-29 17:39 ` Max Kellermann
2025-01-29 17:45 ` Jens Axboe
2025-01-29 18:01 ` Max Kellermann
2025-01-31 16:13 ` Jens Axboe
2025-02-01 15:25 ` Jens Axboe
2025-02-01 15:30 ` Max Kellermann
2025-02-01 15:38 ` Jens Axboe
2025-01-29 19:30 ` Pavel Begunkov
2025-01-29 19:43 ` Max Kellermann
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