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Date: Mon, 22 Sep 2008 22:31:15 -0400 From: Mathieu Desnoyers <compudj@...stal.dyndns.org> To: Darren Hart <darren@...art.com> Cc: Roland Dreier <rdreier@...co.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Masami Hiramatsu <mhiramat@...hat.com>, Martin Bligh <mbligh@...gle.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, "Frank Ch. Eigler" <fche@...hat.com>, systemtap-ml <systemtap@...rces.redhat.com> Subject: Re: Unified tracing buffer * Darren Hart (darren@...art.com) wrote: > On Mon, Sep 22, 2008 at 7:02 PM, Mathieu Desnoyers <compudj@...stal.dyndns.org> > > So only in the specific case of instrumentation of things like locking, > > where it is possible to insure that instrumentation is synchronized with > > the instrumented operation, does it make a difference to choose the TSC > > (which implies a slight delta between the TSCs due to cache line delays > > at synchronization and delay due to TSCs drifts caused by temperature) > > over an atomic increment. > > > > Hrm, i think that overlooks the other reason to use a time based counter over > an atomic increment: you might care about time. Perhaps one might be less > concerned with actual order tightly grouped events and more concerned with the > actual time delta between more temporally distant events. In that case, using > a clocksource would still be valuable. Although admitedtly the caller could > embed that in their payload, but since we seem to agree we need some kind of > counter, the time-based counter appears to be the most flexible. > > Thanks, > See my answer to Linus for a proposal on how to do both :) Mathieu > -- > Darren Hart > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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