Messages in this thread | | | From | Sven Schnelle <> | Subject | Re: [PATCH 0/3] entry: inline syscall enter/exit functions | Date | Thu, 14 Dec 2023 09:24:17 +0100 |
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Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, Dec 05, 2023 at 02:30:12PM +0100, Sven Schnelle wrote: >> Hi List, >> >> looking into the performance of syscall entry/exit after s390 switched >> to generic entry showed that there's quite some overhead calling some >> of the entry/exit work functions even when there's nothing to do. >> This patchset moves the entry and exit function to entry-common.h, so >> non inlined code gets only called when there is some work pending. > > So per that logic you wouldn't need to inline exit_to_user_mode_loop() > for example, that's only called when there is a EXIT_TO_USER_MODE_WORK > bit set. > > That is, I'm just being pedantic here and pointing out that your > justification doesn't cover the extent of the changes. > >> I wrote a small program that just issues invalid syscalls in a loop. >> On an s390 machine, this results in the following numbers: >> >> without this series: >> >> # ./syscall 1000000000 >> runtime: 94.886581s / per-syscall 9.488658e-08s >> >> with this series: >> >> ./syscall 1000000000 >> runtime: 84.732391s / per-syscall 8.473239e-08s >> >> so the time required for one syscall dropped from 94.8ns to >> 84.7ns, which is a drop of about 11%. > > That is obviously very nice, and I don't immediately see anything wrong > with moving the lot to header based inlines. > > Thomas?
Thomas, any opinion on this change?
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