lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 27 Mar 2012 21:38:18 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Arun Sharma <asharma@...com> Cc: Frederic Weisbecker <fweisbec@...il.com>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Arnaldo Carvalho de Melo <acme@...hat.com>, Mike Galbraith <efault@....de>, Paul Mackerras <paulus@...ba.org>, Stephane Eranian <eranian@...gle.com>, Namhyung Kim <namhyung.kim@....com>, Tom Zanussi <tzanussi@...il.com>, linux-perf-users@...r.kernel.org Subject: Re: [PATCH] perf: Add a new sort order: SORT_INCLUSIVE (v4) On Tue, 2012-03-27 at 11:09 -0700, Arun Sharma wrote: > On 3/24/12 7:14 PM, Frederic Weisbecker wrote: > > >> The other problem in branch stacks/LBR is that they're > >> sampled branches. Just because I got a sample with: > >> > >> a -> b > >> b -> c > >> > >> doesn't necessarily mean that the callchain was a -> b -> c. > > > > Not sure what you mean. If you have a -> b, b -> c in single > > LBR sample it means you got a -> b -> c. > > > > I was going by Stephane's commit message here: > > http://article.gmane.org/gmane.linux.kernel/1236999 > > > Statistical sampling of taken branch should not be confused > > for branch tracing. Not all branches are necessarily captured > > Stephane, could you please explain if the 16 filtered branches in LBR > are guaranteed to be from a given callchain to the leaf function? My > understanding is that it's not. > > callchain1: a -> b -> d -> e (sample a->b) > callchain2: a -> c -> b -> f (sample b->f) > > on PMU interrupt can we end up with: > > b -> f <- top of stack > a -> b > ... > > even though a -> b -> f can never happen in the actual program flow? Right, so the LBR is a queue not a stack. A program like: foo() { bar1(); bar2(); } will, using the lbr, look like: foo->bar1->bar2 (if you filter returns), or foo->bar1->foo+x->bar2 if you include returns. A callchain is a pure stack, a return pops the top most entry, the above program can only give 3 possible callchains: a) foo b) foo, bar1 c) foo, bar2 Furthermore, the LBR is about any branch, callchains are about function calls. -- 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/
Powered by blists - more mailing lists