From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Hui Tang <tanghui20@huawei.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [bug-report] possible performance problem in ret_to_user_from_irq
Date: Tue, 3 Jan 2023 10:06:42 +0000 [thread overview]
Message-ID: <Y7P+MjPNA6Tg8JBr@shell.armlinux.org.uk> (raw)
In-Reply-To: <7ecb8f3c-2aeb-a905-0d4a-aa768b9649b5@huawei.com>
On Mon, Dec 26, 2022 at 04:45:20PM +0800, Hui Tang wrote:
> hi folks.
>
> I found a performance problem which is introduced by commit
> 32d59773da38 ("arm: add support for TIF_NOTIFY_SIGNAL").
> After the commit, any bit in the range of 0..15 will cause
> do_work_pending() to be invoked. More frequent do_work_pending()
> invoked possible result in worse performance.
>
> Some of the tests I've done， as follows:
> lmbench test base with patch
> ./lat_ctx -P 1 -s 0 2 7.3167 11.04
> ./lat_ctx -P 1 -s 16 2 8.0467 14.5367
> ./lat_ctx -P 1 -s 64 2 7.8667 11.43
> ./lat_ctx -P 1 -s 16 16 16.47 18.3667
> ./lat_pipe -P 1 28.1671 44.7904
>
> libMicro-0.4.1 test base with patch
> ./cascade_cond -E -C 200\
> -L -S -W -N "c_cond_1" -I 100 286.3333 358
>
> When I adjust test bit, the performance problem gone.
> - movs r1, r1, lsl #16
> + ldr r2, =#_TIF_WORK_MASK
> + tst r1, r2
>
> Does anyone have a good suggestion for this problem?
> should just test _TIF_WORK_MASK, as before?
I think it should be fine - but I would suggest re-organising the
TIF definitions so that those TIF bits that shouldn't trigger
do_work_pending are not in the first 16 bits.
Note that all four bits in _TIF_SYSCALL_WORK need to stay within
an 8-bit even-bit-aligned range, so the value is suitable for an
immediate assembly constant.
I'd suggest moving the TIF definitions for 20 to 19, and 4..7 to
20..23, and then 8 to 4.
Thanks.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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next prev parent reply other threads:[~2023-01-03 15:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-26 8:45 [bug-report] possible performance problem in ret_to_user_from_irq Hui Tang
2023-01-03 10:06 ` Russell King (Oracle) [this message]
2023-01-03 14:25 ` Jens Axboe
2023-01-03 14:34 ` Russell King (Oracle)
2023-01-03 14:59 ` Jens Axboe
2023-01-04 1:31 ` Hui Tang
2023-01-04 7:04 ` Hui Tang
2023-01-04 14:45 ` Jens Axboe
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