Messages in this thread | | | Date | Thu, 26 Feb 2009 21:06:24 +0900 (JST) | Subject | Re: [PATCH] cpuacct: add a branch prediction | From | "KAMEZAWA Hiroyuki" <> |
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Peter Zijlstra wrote: > On Thu, 2009-02-26 at 20:17 +0900, KAMEZAWA Hiroyuki wrote: >> Peter Zijlstra wrote: >> > On Thu, 2009-02-26 at 19:28 +0900, KAMEZAWA Hiroyuki wrote: >> > >> >> Taking hierarchy mutex while reading will make read-side stable. >> > >> > We're talking about scheduling here, taking a mutex to stop scheduling >> > won't work, nor will it be acceptible to use anything that will. >> > >> No mutex is necessary, anyway. >> hierarchy-walker function completely works well under rcu read lock, >> if small jitter is allowed. > > Right, should be doable -- and looking at the code, we have this > horrible 32 bit exception in there that locks the rq in order to read > the 64bit value. > > Would be grand to get rid of that,. how bad would it be for userspace to > get the occasionally fubarred value? > From view of user-support saler, if terrible broken value is reported, it will be user-incident and annoy me(us) ;)
I'd like to get rid of rq->lock, too..Hmm.. some routine like atomic64_read() can help this ? (But I don't want to use atomic_t here..)
> But aside from that, the cpu controller itself is also summing directly > up the hierarchy, so cpuacct doing the same doesn't seem odd. > I'll post some idea if I can think of something reasonable. But I tend to hesitate to modify sched.c ;)
Thanks, -Kame
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