Date: Wed, 17 Jan 2007 23:38:06 -0800 From: Suleiman Souhlal <ssouhlal@FreeBSD.org> To: Bruce Evans <bde@zeta.org.au> Cc: Maxim Sobolev <sobomax@freebsd.org>, Ivan Voras <ivoras@fer.hr>, Attilio Rao <attilio@freebsd.org>, freebsd-current@freebsd.org, freebsd-arch@freebsd.org Subject: Re: [PATCH] Mantaining turnstile aligned to 128 bytes in i386 CPUs Message-ID: <45AF23DE.6030801@FreeBSD.org> In-Reply-To: <20070118113831.A11834@delplex.bde.org> References: <3bbf2fe10607250813w8ff9e34pc505bf290e71758@mail.gmail.com> <3bbf2fe10607281004o6727e976h19ee7e054876f914@mail.gmail.com> <3bbf2fe10701160851r79b04464m2cbdbb7f644b22b6@mail.gmail.com> <20070116154258.568e1aaf@pleiades.nextvenue.com> <b1fa29170701161355lc021b90o35fa5f9acb5749d@mail.gmail.com> <eoji7s$cit$2@sea.gmane.org> <b1fa29170701161425n7bcfe1e5m1b8c671caf3758db@mail.gmail.com> <eojlnb$qje$1@sea.gmane.org> <3bbf2fe10701161525j6ad9292y93502b8df0f67aa9@mail.gmail.com> <45AD6DFA.6030808@FreeBSD.org> <3bbf2fe10701161655p5e686b52n7340b3100ecfab93@mail.gmail.com> <200701172022.l0HKMYV8053837@apollo.backplane.com> <20070118113831.A11834@delplex.bde.org>
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Bruce Evans wrote: > On Wed, 17 Jan 2007, Matthew Dillon wrote: >> * No extranious memory writes, no uncached extranious memory reads. >> If you do any writes to memory other then to the copy destination >> in your copy loop you screw up the cpu's write fifo and destroy >> performance. >> >> Systems are so sensitive to this that it is even better to spend the >> time linearly mapping large copy spaces into KVM and do a single >> block copy then to have an inner per-PAGE loop. > > > I haven't tried this, but have seen and partly worked sensitivity to > linear KVA maps not being physically (non)linear enough. Some CPUs > and/or memory systems are remarkably sensitive to bank interleave. > FreeBSD's page coloring doesn't know anything about banks, and > accidentally starts up with perfect miscoloring for banks. This can > make a difference of 30% for bzero bandwidth in benchmarks (not so > much for bcopy bandwidth, and an insignificant amount for normal use). > After the system warms up, the coloring becomes random with respect > to banks, and random coloring works much better than perfect miscoloring. About page coloring: Don't amd64 CPUs have virtually indexed, physically tagged caches? If so, wouldn't it make sense to turn off page coloring, since it's useless for virtually indexed caches (and probably hurts things a bit)? -- Suleiman
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