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charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7ecb8f3c-2aeb-a905-0d4a-aa768b9649b5@huawei.com> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 doneļ¼Œ 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/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!