On Mon, Jan 3, 2011 at 3:45 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Mon, 2011-01-03 at 09:40 +0200, Pekka Enberg wrote: >> Hi, >> >> On Mon, Jan 3, 2011 at 8:48 AM, Theodore Ts'o <tytso@xxxxxxx> wrote: >> >> Given the patches being busily submitted by trivial patch submitters to >> >> make use kmem_cache_zalloc(), et. al, I believe we should remove the >> >> unlikely() tests around the (gfp_flags & __GFP_ZERO) tests, such as: >> >> >> >> - if (unlikely((flags & __GFP_ZERO) && objp)) >> >> + if ((flags & __GFP_ZERO) && objp) >> >> memset(objp, 0, obj_size(cachep)); >> >> >> >> Agreed? If so, I'll send a patch... >> >> On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote: >> > I support it. >> >> I guess the rationale here is that if you're going to take the hit of >> memset() you can take the hit of unlikely() as well. We're optimizing >> for hot call-sites that allocate a small amount of memory and >> initialize everything themselves. That said, I don't think the >> unlikely() annotation matters much either way and am for removing it >> unless people object to that. >> >> On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote: >> > Recently Steven tried to gather the information. >> > http://thread.gmane.org/gmane.linux.kernel/1072767 >> > Maybe he might have a number for that. >> >> That would be interesting, sure. > > Note, you could do it yourself too. Just enable: > > Kernel Hacking -> Tracers -> Branch Profiling > (Trace likely/unlikely profiler) > > CONFIG_PROFILE_ANNOTATED_BRANCHES > > Then search /debug/tracing/trace_stats/branch_annotated. > > (hmm, the help in Kconfig is wrong, I need to fix that) > > > Anyway, here's my box. I just started it an hour ago, and have not been > doing too much on it yet. But here's what I got (using SLUB) > > > correct incorrect % Function File Line > ------- --------- - -------- ---- ---- > 6890998 2784830 28 slab_alloc slub.c 1719 > > That's incorrect 28% of the time. Thanks! AFAICT, that number is high enough to justify removing the unlikely() annotations, no? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href