Date: Mon, 11 Dec 2017 17:22:19 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: rgrimes@freebsd.org Cc: Conrad Meyer <cem@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r326758 - in head/sys/i386: conf include Message-ID: <20171211152219.GL2272@kib.kiev.ua> In-Reply-To: <201712111509.vBBF9Aha081695@pdx.rh.CN85.dnsmgr.net> References: <201712110432.vBB4WbnE021090@repo.freebsd.org> <201712111509.vBBF9Aha081695@pdx.rh.CN85.dnsmgr.net>
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On Mon, Dec 11, 2017 at 07:09:10AM -0800, Rodney W. Grimes wrote: > The current comment about a pcb, I thought that code was changed > so we only put the pointer to a pcb on the stack. pcb is on top of the stack, followed by the userspace FPU registers save area. I do not see any sense in existence of pcb in modern kernel, it is a remnant of the user area that was swappable. Currently pcb is swappable as well, but the value of this is much less then the overhead we pay by the stack space reduction. FPU save area is the on of the problem which makes us increase the amd64 stack size, AVX or even AVX512 make the things much worse. It is unlikely that somebody would run 32bit kernel on machine capable of that extensions, i.e. Haswell or Skylake.
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