Date: Wed, 7 Dec 2016 11:41:21 -0800 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Mateusz Guzik <mjguzik@gmail.com> Cc: Fabien Thomas <fabient@FreeBSD.org>, svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r309143 - head/sys/libkern Message-ID: <20161207194121.GM27748@FreeBSD.org> In-Reply-To: <20161125160010.GA3307@dft-labs.eu> References: <201611251349.uAPDnX09042110@repo.freebsd.org> <20161125160010.GA3307@dft-labs.eu>
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On Fri, Nov 25, 2016 at 05:00:10PM +0100, Mateusz Guzik wrote: M> On Fri, Nov 25, 2016 at 01:49:33PM +0000, Fabien Thomas wrote: M> > Author: fabient M> > Date: Fri Nov 25 13:49:33 2016 M> > New Revision: 309143 M> > URL: https://svnweb.freebsd.org/changeset/base/309143 M> > M> > Log: M> > In a dual processor system (2*6 cores) during IPSec throughput tests, M> > we see a lot of contention on the arc4 lock, used to generate the IV M> > of the ESP output packets. M> > M> > The idea of this patch is to split this mutex in order to reduce the M> > contention on this lock. M> > M> > +MALLOC_DEFINE(M_ARC4RANDOM, "arc4random", "arc4random structures"); M> > M> > -static u_int8_t arc4_randbyte(void); M> > +struct arc4_s { M> > + u_int8_t i, j; M> > + int numruns; M> > + u_int8_t sbox[256]; M> > + time_t t_reseed; M> > + M> > + struct mtx mtx; M> > +}; M> > + M> M> Why is the lock at the end? Right now you got false sharing with the M> next entry. M> M> That said, I suggest: M> 1. moving thelock to the beginning M> 2. annotating the struct with __aligned(CACHE_LINE_SIZE) It could be even better not to allocate them with regular malloc at all, but to put them into the per cpu areas. I haven't tried, but looks like the DPCPU mechanism defined in sys/pcpu.h would fit that well. -- Totus tuus, Glebius.
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