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Subject[bug-report] possible performance problem in ret_to_user_from_irq
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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?

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