On Wed, Mar 23, 2011 at 6:48 PM, Linus Torvalds
[off-list ref] wrote:

On Wed, Mar 23, 2011 at 8:37 AM, Tejun Heo [off-list ref] wrote:

quoted

Currently, mutex_trylock() doesn't use adaptive spinning. =C2=A0It t=

ries

quoted

just once. =C2=A0I got curious whether using adaptive spinning on
mutex_trylock() would be beneficial and it seems so, at least for
btrfs anyway.

Hmm. Seems reasonable to me.

TAS/spin with exponential back-off has been preferred locking approach
in Postgres (and I believe other DBMSes) for years, at least since '04
when I had last touched Postgres code. Even with 'false negative' cost
in user-space being much higher than in the kernel, it's still just a
question of scale (no wonder measurable improvement here is reported
from dbench on SSD capable of few dozen thousand IOPS).

Regards,
Andrey

The patch looks clean, although part of that is just the mutex_spin()
cleanup that is independent of actually using it in trylock.

So no objections from me.

=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=

Linus

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