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Re: [Qemu-devel] [PATCH] Huge TLB performance improvement
From: |
Thiemo Seufer |
Subject: |
Re: [Qemu-devel] [PATCH] Huge TLB performance improvement |
Date: |
Sun, 12 Nov 2006 14:29:38 +0000 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Paul Brook wrote:
> On Sunday 12 November 2006 11:49, Laurent Desnogues wrote:
> > Daniel Jacobowitz a écrit :
> > > Straight qemu with my previously posted MIPS patches takes 6:13 to
> > > start and reboot a MIPS userspace (through init, so lots of fork/exec).
> > >
> > > Thiemo's patch, which flushes the whole jump buffer, cuts it to 1:40.
> > >
> > > A patch which finds the entries which need to be flushed more
> > > efficiently cuts it to 1:21.
> > >
> > > A patch which flushes up to 1/32nd of the jump buffer indiscriminately
> > > cuts it to 1:11-1:13.
> >
> > Warning: I don't know anything about the Qemu MMU implementation
> > so this question is perhaps stupid :)
> >
> > Did you try to benchmark some user space applications with the
> > various implementations you propose? The boot of a Linux kernel
> > is quite heavy on various kinds of flushes and so is very
> > different from "standard" applications.
>
> MIPS is different because it has a relatively small software managed TLB.
JFTR, increasing the TLB size from 16 to 64 entries made no performance
difference whatsoever.
> Other targets have a hardware managed TLB. On a hardware managed TLB the OS
> treats it as if it were infinite size, and invalidation only occurs when a OS
> changes the mappings. On a software managed TLB "flushes" are more likely to
> occur during normal operation as TLB slots are reused.
The excessive flushing for mips happens because Qemu doesn't properly
model the hardware's ASID handling.
Thiemo
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/05
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/11
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Laurent Desnogues, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Thiemo Seufer, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Paul Brook, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement,
Thiemo Seufer <=
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Paul Brook, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Thiemo Seufer, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Dirk Behme, 2006/11/12
- Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Daniel Jacobowitz, 2006/11/12
Re: [Qemu-devel] [PATCH] Huge TLB performance improvement, Paul Brook, 2006/11/12