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William Lee Irwin III <wli@holomorphy.com> wrote: >> read_proc_profile()>> does not flush the per-cpu hashtables because flushing may cause >> timeslice overrun on the systems where prof_buffer cacheline bounces >> are so problematic as to livelock the timer interrupt. On Mon, Sep 13, 2004 at 10:05:21PM -0700, Andrew Morton wrote: > That's a bit of a problem, isn't it? As we can accumulate an arbitrarily > large number of hits within the hash table is it not possible that the > /proc/profile results could be grossly inaccurate?> If you had two front-ends per cpu to the profiling buffer then the CPU > which is running the /proc/profile read could tell all the other CPUs to > flip to their alternate buffer and can then perform accumulation at its > leisure. This is superior to no flushing; I'll implement that and send out an incremental update (or if preferred, an update of this patch). On Mon, Sep 13, 2004 at 10:05:21PM -0700, Andrew Morton wrote: > How does oprofile get around this? I guess in most modes the CPUs are not > synchronised.> One wonders how long we should keep flogging the /prof/profile profiling > code. What systems are seeing this livelock? The original bits were merely a consolidation extracted from a since- dropped feature patch and an unrelated feature patch from mingo and arjanv; this is an unrelated fix for SGI's stability issue on larger Altixen. I personally intend to do no further adjustments. -- wli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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