On Wed, 23 May 2007, Peter Zijlstra wrote: > On Wed, 2007-05-23 at 12:11 -0400, Jason Baron wrote: > > On Wed, 23 May 2007, Peter Zijlstra wrote: > > > > > On Wed, 2007-05-23 at 10:40 -0400, Jason Baron wrote: > > > > On Wed, 23 May 2007, Peter Zijlstra wrote: > > > > > > > > > Count lock contention events per lock class. Additionally track the > > > > > first four > > > > > callsites that resulted in the contention. > > > > > > > > > > > > > I think that we need the total number of locking calls, not just the > > > > total > > > > number of *contended* locking calls, in order to make the data > > > > significant. Same for waittime. Yes, this pollutes the fastpath. In the > > > > contention case, its one extra addition, and for the waittime, its a > > > > call > > > > the sched_clock(). I don't think that's too much to pay for much more > > > > meaningful data. > > > > > > The holdtime statistics add these numbers. > > > > > > > ok, i see what you are saying...however, the 'waittime' statistic as > > implemented, is only recorded when we don't get the lock immediately. > > Thus, it's really measuring the waittime when there is lock contention. I > > understand that in the non-contended case we are only talking a a few > > cycles, but the fact that the non-contended case is not counted as another > > waittime of even zero length (so no measurement is required), might skew > > the stats a bit. For examples, if there was a lock that was almost never > > contended but one time happened to be contended for a long time, its > > average wait time would look really high. > > I'm not seeing how or why this is a problem. The number of contentions > is reported on the same line, so it should be obvious. > > Your definition of wait-time is also obtainable from the numbers, one > would just divide waittime-total by acquisitions, instead of > contentions. >
agreed, I just want to point out that under my definition of waitime, I would have to make the assumption that the waittime is 0 for a lock that is acquired without fallback to the slowpath. For a spinlock acquisition, this is likely a fair assumption, however the trylock path for semaphores can be longer. Acked-by: Jason Baron <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/