[Bug 71641] Unreasonable performance degradation in ext4 with full data journaling

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=71641

--- Comment #8 from Theodore Tso <tytso@mit.edu> ---
it's clear this isn't going to get performance up to 1.1 GB/s, but I'm curious
how much setting JBD2_NR_BATCH changes things at 512 and 1024 and possibly even
2048.   Once it no longer maters a difference, if you could do another
blktrace, and also gather lock_stat information, that would be useful.

To gather lock_stat information, enable CONFIG_LOCK_STAT, and then "echo 0  >
/proc/lock_stat" before you start the workload, and then capture the output of
/proc/lock_stat after you finish running your workload/benchmark.

If you also regather numbers with lock_stat enabled on a stock 3.11 kernel (and
also get a /proc/lock_stat report from a stock 3.11 kernel, with and without
data=journal), that would be useful.

If it turns out that there is some lock contention going on with some of the
jbd2 spinlocks, there are some patches queued for 3.15 that I may have to ask
you to try (which will mean going to something like 3.14-rc7 plus some
additional patches from the ext4 git tree).

Thanks for your benchmarking!

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