Messages in this thread | | | Date | Sat, 14 Feb 2009 10:32:13 +0100 | From | Andi Kleen <> | Subject | Re: Fwd: [PATCH] Implement barrier support for single device DM devices |
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On Sat, Feb 14, 2009 at 12:26:05AM +0100, Mat wrote: > Hi Andi, > > any news on this patch ?
It's in mainline as of 2.6.29-rc4.
> from what I saw it isn't included in mainline yet, if it is already > please point to the kernel-config option where to enable it
It's always enabled for simple DM remapped devices given that its conditions (only single underlying device etc.) are true.
> heavy flush, write operations; especially on amd64/X64: > http://forums.gentoo.org/viewtopic-t-482731.html > > I'm not sure if it's possible but I believe it could also be related > to filesystems switching to synchronous writes (non-barrier > write-mode) when the underlying partition is a LUKS-partition and
Note that my patch doesn't enable barriers for LUKS/dm_crypt, that would be another patch which is not currently submtted.
> therefore > decreasing performance (I'm not a kernel-hacker so I don't know if > there's a possible correlation here)
You can find out by testing it without LUKS, but enabling/disabling barriers on a file system and see how much difference it makes. That would be better than speculating.
> > some factors I noticed having an impact on that are:
How did you determine that? Did you run some repeatable benchmark that gave different numbers?
> - the i/o scheduler hardly makes a change > - elder boxes with PCI (non-PCIe) can be "fixed" with some latency-tweaks: > setpci -v -d *:* latency_timer=b0
You realize that the PCI latency has nothing to do with IO scheduler delays? It's very unlikely that there is a correlation there. Please double check these results.
-Andi -- ak@linux.intel.com -- Speaking for myself only.
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