On Monday 15 February 2010, Mike Galbraith wrote: > On Mon, 2010-02-15 at 00:38 +0100, Rafael J. Wysocki wrote: > > This message has been generated automatically as a part of a summary report > > of recent regressions. > > > > The following bug entry is on the current list of known regressions > > from 2.6.32. Please verify if it still should be listed and let the tracking team > > know (either way). > > > > > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=15044 > > Subject : Much higher wakeups for "<kernel IPI> : Rescheduling interrupts" since 2.6.32.2 > > Submitter : Roman Mamedov <roman@xxxxxxxx> > > Date : 2010-01-11 02:58 (35 days old) > > First-Bad-Commit: http://git.kernel.org/git/linus/a1f84a3ab8e002159498814eaa7e48c33752b04b > > I don't know that this should be carried as a regression. > > Yes, the code in question increases cross cpu wakeups, but that's the > entire point. If there is any overlap in execution larger than the cost > of running a scheduler on another core, that time can be converted to > throughput. > > Tip AF_UNIX lmbench numbers show that throughput gain being realized, > TCP numbers below that (x) show what can be had for apps which do a lot > of what that microbenchmark does, given a tiny enabler patchlet. > > *Local* Communication bandwidths in MB/s - bigger is better > ----------------------------------------------------------------------------- > Host OS Pipe AF TCP File Mmap Bcopy Bcopy Mem Mem > UNIX reread reread (libc) (hand) read write > --------- ------------- ---- ---- ---- ------ ------ ------ ------ ---- ----- > marge 2.6.31.9-smp 2853 2923 1132 2829.3 4761.9 1235.0 1234.4 4472 1683. > marge 2.6.31.9-smp 2839 2921 1141 2846.5 4779.8 1242.5 1235.9 4455 1684. > marge 2.6.31.9-smp 2838 2935 751. 2838.5 4820.0 1243.6 1235.0 4472 1684. > marge 2.6.33-tip-smp 3057 5166 859. 2760.2 4827.8 1481.1 1466.1 4499 1811. > marge 2.6.33-tip-smp 1796 5165 1257 2748.6 4817.4 1481.1 1464.8 4487 1806. > marge 2.6.33-tip-smp 3055 5175 1262 2763.4 4812.4 1483.9 1462.7 4477 1810. > marge 2.6.33-tip-smpx 3063 5140 2940 2811.1 4740.0 1235.8 1237.0 4433 1673. > marge 2.6.33-tip-smpx 3065 5205 2945 2836.3 4794.4 1243.6 1233.7 4293 1686. > marge 2.6.33-tip-smpx 3058 5181 2940 2785.4 4700.2 1243.9 1234.5 4415 1682. > > (1. tip memory numbers are phase-of-moon anomaly.. irrelevant here) > (2. pipe numbers are only possible with pipe buffer increase patch in > tip. Often, pipes are truly synchronous, so waking cross CPU is small > loss. In tip, it's a win because of optimistic mutex spin.. context > switch cost is converted to throughput. That throughput gain also > cannot be had if you don't do the cross cpu wakeup to get the ball > rolling. The code in question is acting as enabler for spintex.) > > So yeah, the code in question _will_ cause more cross CPU wakeups, and > it _may_ cost power. It may _save_ power by getting the job done more > efficiently. Dunno. > > Regression? Depends on what you're measuring. OK, so I'm going to close this report as "documented", since this is intentional behavior. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
