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SubjectRe: [PATCH] btrfs: lower metadata writeback threshold on low dirty threshold
On Thu, May 03, 2012 at 11:43:11AM +0800, Fengguang Wu wrote:
> This helps write performance when setting the dirty threshold to tiny numbers.
>
> 3.4.0-rc2 3.4.0-rc2-btrfs4+
> ------------ ------------------------
> 96.92 -0.4% 96.54 bay/thresh=1000M/btrfs-100dd-1-3.4.0-rc2
> 98.47 +0.0% 98.50 bay/thresh=1000M/btrfs-10dd-1-3.4.0-rc2
> 99.38 -0.3% 99.06 bay/thresh=1000M/btrfs-1dd-1-3.4.0-rc2
> 98.04 -0.0% 98.02 bay/thresh=100M/btrfs-100dd-1-3.4.0-rc2
> 98.68 +0.3% 98.98 bay/thresh=100M/btrfs-10dd-1-3.4.0-rc2
> 99.34 -0.0% 99.31 bay/thresh=100M/btrfs-1dd-1-3.4.0-rc2
> ==> 88.98 +9.6% 97.53 bay/thresh=10M/btrfs-10dd-1-3.4.0-rc2
> ==> 86.99 +13.1% 98.39 bay/thresh=10M/btrfs-1dd-1-3.4.0-rc2
> ==> 2.75 +2442.4% 69.88 bay/thresh=1M/btrfs-10dd-1-3.4.0-rc2
> ==> 3.31 +2634.1% 90.54 bay/thresh=1M/btrfs-1dd-1-3.4.0-rc2

Well, further tests show that it behaves very unstable:

3.4.0-rc2-btrfs4+ 3.4.0-rc2-btrfs5+
------------------------ ------------------------
69.88 +16.4% 81.31 bay/thresh=1M/btrfs-10dd-1-3.4.0-rc2-btrfs4+
71.09 +1.4% 72.05 bay/thresh=1M/btrfs-10dd-2-3.4.0-rc2-btrfs4+
72.60 -1.7% 71.38 bay/thresh=1M/btrfs-10dd-3-3.4.0-rc2-btrfs4+
90.54 -0.9% 89.74 bay/thresh=1M/btrfs-1dd-1-3.4.0-rc2-btrfs4+
89.17 -90.2% ==> 8.71 bay/thresh=1M/btrfs-1dd-2-3.4.0-rc2-btrfs4+
==> 14.96 +495.3% 89.06 bay/thresh=1M/btrfs-1dd-3-3.4.0-rc2-btrfs4+
408.23 +1.0% 412.26 TOTAL write_bw
Where the -btrfs5 kernel has one more patch to remove the write plug.

Thanks,
Fengguang


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