Messages in this thread | | | Date | Thu, 26 Feb 2009 19:50:53 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC][PATCH] signals: don't copy siginfo_t on dequeue |
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* Vegard Nossum <vegard.nossum@gmail.com> wrote:
> >From 60fc9a464377159ab807aec63277d4970019d631 Mon Sep 17 00:00:00 2001 > From: Vegard Nossum <vegard.nossum@gmail.com> > Date: Thu, 26 Feb 2009 19:17:58 +0100 > Subject: [PATCH] signals: don't copy siginfo_t on dequeue > > Instead of copying the siginfo_t whenever a signal is dequeued, just > get the pointer to the struct sigqueue, which can be freed by the > caller when the signal has been delivered. > > We can save kernel text (x86, 32-bit): > > $ scripts/bloat-o-meter vmlinux-unpatched vmlinux > add/remove: 0/0 grow/shrink: 3/7 up/down: 81/-538 (-457) > function old new delta > get_signal_to_deliver 871 922 +51 > release_console_sem 459 481 +22 > generate_resume_trace 611 619 +8 > send_sigqueue 257 253 -4 > vma_adjust 1101 1093 -8 > sys_rt_sigtimedwait 548 531 -17 > dequeue_signal 415 372 -43 > __dequeue_signal 388 259 -129 > signalfd_read 1290 1139 -151 > do_notify_resume 2216 2030 -186 > > And we reduce stack pressure; In handle_signal() (in x86 code), we > replace a siginfo_t (128 bytes) with a pointer (8 bytes on x86_64), > and the same in signalfd_read(). > > There is a slight slowdown (2.02% relative increase in CPU time): > > unpatched patched > ---------------------------------------- > mean: 3.078500 3.140800 > stddev: 0.074624 0.168989 > > (Numbers are: CPU time in seconds, for two processes to > ping-pong in total 655360 SIGUSR1/SIGUSR2 signals between each > other. This was repeated 100 times for each kernel.)
hm, does this SIGUSR1/SIGUSR2 test actually make use siginfo?
I.e. shouldnt we have seen a speedup, due to not having to copy the siginfo structure?
Ingo
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