Messages in this thread | | | Subject | Re: [bug-report] possible performance problem in ret_to_user_from_irq | From | Hui Tang <> | Date | Wed, 4 Jan 2023 09:31:39 +0800 |
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On 2023/1/3 22:59, Jens Axboe wrote: > On 1/3/23 7:34?AM, Russell King (Oracle) wrote: >> On Tue, Jan 03, 2023 at 07:25:26AM -0700, Jens Axboe wrote: >>> On 1/3/23 3:06?AM, Russell King (Oracle) wrote: >>>> 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. >>> >>> Like this? >>> >>> diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h >>> index aecc403b2880..7f092cb55a41 100644 >>> --- a/arch/arm/include/asm/thread_info.h >>> +++ b/arch/arm/include/asm/thread_info.h >>> @@ -128,15 +128,16 @@ extern int vfp_restore_user_hwstate(struct user_vfp *, >>> #define TIF_NEED_RESCHED 1 /* rescheduling necessary */ >>> #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */ >>> #define TIF_UPROBE 3 /* breakpointed or singlestepping */ >>> -#define TIF_SYSCALL_TRACE 4 /* syscall trace active */ >>> -#define TIF_SYSCALL_AUDIT 5 /* syscall auditing active */ >>> -#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */ >>> -#define TIF_SECCOMP 7 /* seccomp syscall filtering active */ >>> -#define TIF_NOTIFY_SIGNAL 8 /* signal notifications exist */ >>> +#define TIF_NOTIFY_SIGNAL 4 /* signal notifications exist */ >>> >>> #define TIF_USING_IWMMXT 17 >>> #define TIF_MEMDIE 18 /* is terminating due to OOM killer */ >>> -#define TIF_RESTORE_SIGMASK 20 >>> +#define TIF_RESTORE_SIGMASK 19 >>> +#define TIF_SYSCALL_TRACE 20 /* syscall trace active */ >>> +#define TIF_SYSCALL_AUDIT 21 /* syscall auditing active */ >>> +#define TIF_SYSCALL_TRACEPOINT 22 /* syscall tracepoint instrumentation */ >>> +#define TIF_SECCOMP 23 /* seccomp syscall filtering active */ >>> + >>> >>> #define _TIF_SIGPENDING (1 << TIF_SIGPENDING) >>> #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) >> >> Yep, LGTM, thanks. > > Hui Tang, can you give it a whirl? Just checked and it applies to > 5.10-stable as well, just with a slight offset.
Okay, I'll test it today.
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