Re: [bug-report] possible performance problem in ret_to_user_from_irq
From: Hui Tang
Date: Wed Jan 04 2023 - 02:04:34 EST
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.
With the latest patch, the testcase rusults shown in the 'new patch' column.
I also retested previous commit of 32d59773da38, the results shown in the 'base' column.
lmbench test base 32d59773da38 new patch
./lat_ctx -P 1 -s 0 2 8.04 11.04 8.25
./lat_ctx -P 1 -s 16 2 9.08 14.5367 9.26
./lat_ctx -P 1 -s 64 2 8.78 11.43 8.71
./lat_ctx -P 1 -s 16 16 17.22 18.3667 17.32
./lat_pipe -P 1 43.5021 44.7904 41.3729
libMicro-0.4.1 test base 32d59773da38 new patch
./cascade_cond -E -C 200\
-L -S -W -N "c_cond_1" -I 100 281 358 281
The performance problem also seem to gone with the latest patch, thanks.