Date: Mon, 7 Mar 2011 13:24:13 +0000 From: Alexander Best <arundel@freebsd.org> To: Chagin Dmitry <dchagin@freebsd.org> Cc: freebsd-emulation@freebsd.org Subject: Re: regarding issues with futexes and multiple threads Message-ID: <20110307132413.GA72267@freebsd.org> In-Reply-To: <20110304174637.GA8522@dchagin.static.corbina.ru> References: <20110303212051.GA54978@freebsd.org> <20110304061328.GA4073@dchagin.static.corbina.ru> <20110304110843.GA65337@freebsd.org> <20110304174637.GA8522@dchagin.static.corbina.ru>
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On Fri Mar 4 11, Chagin Dmitry wrote: > On Fri, Mar 04, 2011 at 11:08:43AM +0000, Alexander Best wrote: > > On Fri Mar 4 11, Chagin Dmitry wrote: > > > On Thu, Mar 03, 2011 at 09:20:51PM +0000, Alexander Best wrote: > > > > hi there, > > > > > > > > i've been investigating this issue for quite a while now and simply wanted to > > > > post some measurements i did. > > > > > > > > basically there's a massive slowdown when a process triggers a lot of threads > > > > which are doing futex operations. the following example is from darren hart's > > > > futex test suite (performance/). the slowdown seems to SMP related. here are > > > > the measurements running with SMP enabled and with kern.smp.disabled=1: > > > > > > > > > > 1) slowdown is expected behaviour. > > > > even if the slowdown is to be expected, looking at the screenshot with the > > top(1) output it seems obvious that there are issues with the current futex > > implementation. > > > > why do you think it's a problem with the futexes? the screenshot was taken with only one flash site opened. so i assumed having so many npviewer instances in state futex and taking up so much ressources is not normaly behavior. i also added a few printf's at the end of the WAIT and WAKE cases in linux_futex.c. this showed that error is almost always != 0. i'll add a few more printf's, since a few futex related changes have been added to HEAD recently. maybe that reveals more details. cheers. alex > > > > 2) is it possible to run this test suite on FreeBSD? > > > > i used emulators/linux_dist-gentoo-stage3 to compile the testsuite and then ran > > it natively under freebsd. if you want to i can send you the file. it's > > > > futex_wait: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped > > > > ah, tests directly calls sys_futex syscall, so can't be used for umtx/futex comparison :) > It would be great to have the same set of tests to compare the linuxulator threads > and the native. > > -- > Have fun! > chd -- a13x
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