Em Tue, Nov 12, 2013 at 03:57:07PM +0100, Peter Zijlstra escreveu: > On Tue, Nov 12, 2013 at 07:46:56AM -0700, David Ahern wrote: > > When recording raw_syscalls for the entire system, e.g., > > perf record -e raw_syscalls:*,sched:sched_switch -a -- sleep 1 > > > > you end up with a negative feedback loop as perf itself calls write() fairly > > often. This patch handles the problem by mmap'ing the file in chunks of 64M > > at > > a time and copies events from the event buffers to the file avoiding write > > system calls. > > You know this completely fails the moment you trace faults, because > every new access to one of those pages (to mark it dirty) will trigger a > fault. And we'll take a bunch more faults -- one for each page -- than > we ever did write() syscalls.
So we should provide a neon lettered warning when doing that, no? :-) > Anyway the over all performance improvements still make it worth it. But > the above seems like a false argument in favour of this. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
