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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 15:26:46 +0000 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Paul Brook wrote:
> > > 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.
>
> Are you sure? IIUC changing the ASID causes a full qemu TLB flush. The code
> we're tweaking here is for single page flush.
I referred with that comment to the general problem of emulating a MMU
with ASIDs in the current qemu fremework.
> Actually that gives me an idea. When a TLB entry with a different ASID gets
> evicted we currently flush that page. This should be a no-op because we
> already did a full flush when the ASID changed.
That's the way the MIPS MMU is supposed to work.
> The other explanation is that the gest OS is manually doing a full TLB flush
> by manually evicting all the TLB entries. I'd hope that a sane guest OS would
> only do that as a last resort though.
Linux/MIPS does this only at a ASID wraparound, which doesn't happen
that often.
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, 2006/11/12
- 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 <=
- 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