Messages in this thread | | | Subject | Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat | From | Peter Zijlstra <> | Date | Fri, 10 Jul 2009 14:52:16 +0200 |
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On Fri, 2009-07-10 at 21:45 +0900, mitake@dcl.info.waseda.ac.jp wrote: > From: Andi Kleen <andi@firstfloor.org> > Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat > Date: Mon, 6 Jul 2009 13:54:51 +0200 > > Thank you for your replying, Peter and Andi. > > > > Maybe re-use the LOCK_CONTENDED macros for this, but I'm not sure we > > > want to go there and put code like this on the lock hot-paths for !debug > > > kernels. > > > > My concern was similar. > > > > I suspect it would be in theory ok for the slow spinning path, but I am > > somewhat concerned about the additional cache miss for checking > > the global flag even in this case. This could hurt when > > the kernel is running fully cache hold, in that the cache miss > > might be far more expensive that short spin. > > Yes, there will be overhead. This is certain. > But there's the radical way to ignore this, > adding subcategory to Kconfig for measuring spinlocks and #ifdef to spinlock.c. > So people who wants to avoid this overhead can disable measurement of spinlocks completely. > > And there's another way to avoid the overhead of measurement. > Making _spin_lock variable of function pointer. > When you don't want to measure spinlocks, > assign _spin_lock_raw() which is equals to current _spin_lock(). > When you want to measure spinlocks, > assign _spin_lock_perf() which locks and measures. > This way will banish the cache miss problem you said. > I think this may be useful for avoiding problem of recursion.
We already have that, its called CONFIG_LOCKDEP && CONFIG_EVENT_TRACING && CONFIG_EVENT_PROFILE, with those enabled you get tracepoints on every lock acquire and lock release, and perf can already use those as event sources.
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