Messages in this thread | | | From | David Sharp <> | Date | Thu, 29 Mar 2012 15:44:41 -0700 | Subject | Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler |
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On Thu, Mar 29, 2012 at 12:12 PM, H. Peter Anvin <hpa@zytor.com> wrote: > On 03/29/2012 12:02 PM, Vaibhav Nagarnaik wrote: >> >> Thanks for the feedback. I had missed this added latency due to this >> patch when tracing is disabled. >> >> To fix that, instead of a TIF flag, I am using a flag in the >> current->trace bitmap. I check that flag before jumping to the tracing >> function. That reduces the latency from 83 ns/call to 74 ns/call. >> > > ANY increase to the fastpath is unacceptable, period.
I think the last 4 ns would probably be eliminated if we could figure out how to call the inline function trace_sys_enter directly instead of through the out-of-line wrapper we had to add to work around the preprocessor magic.
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