Date: Thu, 21 May 2009 10:39:25 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Jeff Roberson <jroberson@jroberson.net> Cc: Ed Schouten <ed@80386.nl>, arch@freebsd.org Subject: Re: lockless file descriptor lookup Message-ID: <alpine.BSF.2.00.0905211038150.25537@fledge.watson.org> In-Reply-To: <alpine.BSF.2.00.0905121430150.981@desktop> References: <alpine.BSF.2.00.0905111720280.981@desktop> <20090512165949.GF58540@hoeg.nl> <alpine.BSF.2.00.0905121430150.981@desktop>
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On Tue, 12 May 2009, Jeff Roberson wrote: >> It's nice to see someone stepped up to implement this. Just out of >> curiosity, have you done any benchmarks to see how many percent of the time >> a thread needs more than one attempt to obtain a valid reference on a >> common workload? >> >> Maybe it would be nice for diagnostic purposes to add two sysctls to obtain >> the amount of successful and unsuccessful attempts. > > I have had trouble triggering it at all in testing. I'd prefer not to > commit the counters because they would re-introduce a global point of cache > contention unless we made them per-cpu. Just as a general observation here: our recent experience with the sysctl counters for microtime(), et al, in the kernel strongly support this view: once the per-CPU allocator is available in the base kernel for 8.0, we should attempt to purge as many of these casually strewn counters in critical paths as we can. Robert N M Watson Computer Laboratory University of Cambridge
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