Messages in this thread | | | Date | Thu, 29 Mar 2012 08:20:31 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler |
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* Vaibhav Nagarnaik <vnagarnaik@google.com> wrote:
> On Wed, Mar 28, 2012 at 7:43 PM, H. Peter Anvin <hpa@zytor.com> wrote: > > But instead you add a penalty for every syscall, even if tracing is > > disabled. Not cool. > > I just ran a small test binary which calls syscall(SYS_getuid) in a > tight loop and calculates the latency per syscall. > > Without my patch: it is 70 ns/call > With my patch: it is 83 ns/call > > So yes, it does add a bit of latency to the syscall even if > tracing is disabled. I wonder if I can change the redirection > function so that it doesn't add so much latency.
There's a really simple rule for anything tracing/debugging related: and syscalls don't add *ANY* kind of latency to the non-tracing case. That is true of the current syscall tracing bits, they work via a TIF flag and don't add any latency.
Thanks,
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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