Date: Tue, 9 Jul 2002 09:10:36 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Peter Wemm <peter@FreeBSD.ORG>, Tor.Egge@cvsup.no.freebsd.org Cc: current@FreeBSD.ORG Subject: Re: [src] cvs commit: src/sys/vm vm_zeroidle.c Message-ID: <200207091610.g69GAawX052365@apollo.backplane.com> References: <20020708230916.B5D4637B4AF@hub.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
I have an idea in regards to the page-zero issue. Presumably we want
to avoid doing an IPI to every cpu to clear the TLB, so what we do
instead is create a lazy TLB clearing mechanism based on the thread.
The scheduler detects the request when it switches the thread in and
invalidates the TLB. Like this:
void
pmap_zero_page(vm_page_t m)
{
vm_offset_t phys = VM_PAGE_TO_PHYS(m);
if (*CMAP2)
panic("pmap_zero_page: CMAP2 busy");
critical_enter(); <<<<<<<<<
*CMAP2 = PG_V | PG_RW | phys | PG_A | PG_M; <<<<<<<<<
invltlb_1pg((vm_offset_t)CADDR2); <<<<<<<<<
curthread->td_lazytlb = PCPU_GET(cpumask); <<<<<<<<<
critical_exit(); <<<<<<<<<
#if defined(I686_CPU)
if (cpu_class == CPUCLASS_686)
i686_pagezero(CADDR2);
else
#endif
bzero(CADDR2, PAGE_SIZE);
*CMAP2 = 0;
}
Then we mod the scheduler to check td_lazytlb against PCPU_GET(cpumask)
when it switches a thread in. If the bit is not set it clears the TLB
and sets the bit.
Now, obviously the above is all just pseudo code. We would want to
properly abstract the API and fields, but I think it solves the problem
quite nicely, at least in concept.
-Matt
:peter 2002/07/08 16:09:11 PDT
:
: Modified files:
: sys/vm vm_zeroidle.c
: Log:
: Turn the zeroidle process off for SMP systems, there is still a possible
: TLB problem when bouncing from one cpu to another (the original cpu will
: not have purged its TLB if the it simply went idle).
:
: Pointed out by: Tor.Egge@cvsup.no.freebsd.org
: Approved by: Tor is never wrong. :-)
:
: Revision Changes Path
: 1.12 +4 -0 src/sys/vm/vm_zeroidle.c
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200207091610.g69GAawX052365>