[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag |
Date: |
Mon, 31 Aug 2009 23:55:16 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Anthony Liguori wrote:
> Christoph Hellwig wrote:
> >>If an unsafe mode is desired (I think it is, for those throwaway
> >>testing VMs, or during OS installs), I suggest adding cache=volatile:
> >>
> >> cache=none
> >> O_DIRECT, fdatasync, advertise volatile write cache
> >>
> >> cache=writethrough
> >> O_SYNC, do not advertise
> >>
> >> cache=writeback
> >> fdatasync, advertise volatile write cache
> >>
> >> cache=volatile
> >> nothing (perhaps fdatasync on QEMU blockdev close)
> >>
> >
> >Fine withe me, let the flame war begin :)
> >
>
> I think we should pity our poor users and avoid adding yet another
> obscure option that is likely to be misunderstood.
>
> Can someone do some benchmarking with cache=writeback and fdatasync
> first and quantify what the real performance impact is?
>
> I think the two reasonable options are 1) make cache=writeback safe,
> avoid a massive perf decrease in the process 2) keep cache=writeback as
> a no-guarantees option.
Right now, cache=writeback does set the bit for SCSI emulation, which makes it
safe for guests which understand that.
Removing that is a regression in safety, not merely a lack of change.
-- Jamie
- [Qemu-devel] [PATCH 0/4] data integrity fixes, Christoph Hellwig, 2009/08/31
- [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Christoph Hellwig, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Jamie Lokier, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Anthony Liguori, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag,
Jamie Lokier <=
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Christoph Hellwig, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Jamie Lokier, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Christoph Hellwig, 2009/08/31
- Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag, Christoph Hellwig, 2009/08/31
[Qemu-devel] [PATCH 2/4] block: use fdatasync instead of fsync, Christoph Hellwig, 2009/08/31
[Qemu-devel] [PATCH 3/4] block: add bdrv_aio_flush operation, Christoph Hellwig, 2009/08/31