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Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O
From: |
Samuel Thibault |
Subject: |
Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O |
Date: |
Mon, 3 Dec 2007 20:26:48 +0100 |
User-agent: |
Mutt/1.5.12-2006-07-14 |
Paul Brook, le Mon 03 Dec 2007 15:39:48 +0000, a écrit :
> I think host caching is still useful enough to be enabled by default, and
> provides a significant performance increase in several cases.
>
> - The guest typically has a relatively small quantity of RAM, compared to a
> modern machine. Allowing the host OS to act as a demand-based L2 cache
> allows this to be used without having to dedicate excessive quantities of ram
> to qemu.
> - I've seen reports that it significantly speeds up the windows installer.
> - Host cache is persistent between multiple qemu runs. f you're doing
> anything
> that requires frequent guest reboots (e.g. kernel debugging) this is going to
> be a huge win.
> - You're running a host OS that has limited or no caching (e.g. DOS).
Yes, and in other cases (e.g. real-production KVM/Xen servers), this is
just cache duplication.
> I'd hope that the host OS would have cache use heuristics that would help
> limit cache pollution.
How could it? It can't detect that the guest also has a buffer/page
cache.
Samuel
- [Qemu-devel] [PATCH 0/2 v2] Open disk images with O_DIRECT, Laurent Vivier, 2007/12/03
- [Qemu-devel] [PATCH 1/2 v2] Add "cache" parameter to "-drive", Laurent Vivier, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Anthony Liguori, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Samuel Thibault, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Paul Brook, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Jamie Lokier, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Anthony Liguori, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Jamie Lokier, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Anthony Liguori, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Laurent Vivier, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Paul Brook, 2007/12/03
- Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O, Anthony Liguori, 2007/12/03