* Byungchul Park <byungchul.park@xxxxxxx> wrote: > On Thu, Oct 19, 2017 at 03:11:12PM +0900, Byungchul Park wrote: > > On Thu, Oct 19, 2017 at 07:57:30AM +0200, Ingo Molnar wrote: > > > > > > * Byungchul Park <byungchul.park@xxxxxxx> wrote: > > > > > > > On Wed, Oct 18, 2017 at 12:09:44PM +0200, Ingo Molnar wrote: > > > > > BTW., have you attempted limiting the depth of the stack traces? I suspect more > > > > > than 2-4 are rarely required to disambiguate the calling context. > > > > > > > > I did it for you. Let me show you the result. > > > > > > > > 1. No lockdep: 2.756558155 seconds time elapsed ( +- 0.09% ) > > > > 2. Lockdep: 2.968710420 seconds time elapsed ( +- 0.12% ) > > > > 3. Lockdep + Crossrelease 5 entries: 3.153839636 seconds time elapsed ( +- 0.31% ) > > > > 4. Lockdep + Crossrelease 3 entries: 3.137205534 seconds time elapsed ( +- 0.87% ) > > > > 5. Lockdep + Crossrelease + This patch: 2.963669551 seconds time elapsed ( +- 0.11% ) > > > > > > I think the lockdep + crossrelease + full-stack numbers are missing? > > > > Ah, the last version of crossrelease merged into vanilla, records 5 > > entries, since I thought it overloads too much if full stack is used, > > and 5 entries are enough. Don't you think so? > > > > > But yeah, looks like single-entry-stacktrace crossrelease only has a +0.2% > > > performance cost (with 0.1% noise), while lockdep itself has a +7.7% cost. > > > > > > That's very reasonable and we can keep the single-entry cross-release feature > > > enabled by default as part of CONFIG_PROVE_LOCKING=y - assuming all the crashes > > > > BTW, is there any crash by cross-release I don't know? Of course, I know > > cases of false positives, but I don't about crash. > > Are you talking about the oops by 'null pointer dereference' by unwinder a > few weeks ago? > > At the time, cross-release was falsely accused. AFAIK, cross-release has > not crashed system yet. I'm talking about the crash fixed here: 8b405d5c5d09: locking/lockdep: Fix stacktrace mess Which was introduced by your patch: ce07a9415f26: locking/lockdep: Make check_prev_add() able to handle external stack_trace ... which was a preparatory patch for cross-release. So 'technically' it's not a cross-release crash, but was very much related. It even says so in the changelog: Actually crossrelease needs to do other than saving a stack_trace. So pass a stack_trace and callback to handle it, to check_prev_add(). ... so let's not pretend it wasn't related, ok? Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
