On Mon, Jun 6, 2016 at 2:13 PM, Waiman Long <[email protected]> wrote:
>
> The tricky part about optimistic spinning in rwsem is that we don't know for
> sure if any of the lock holding readers is running or not.
I'm notm sure how common the reader-vs-writer contention is, at least
for the new inode use. I'm sure you can trigger it with crazy
benchmarks, but I wouldn't worry about it unless people start
complaining.
The writer-writer case is easy to trigger with write-heavy loads (ok,
rename/unlink in this case). Are there real loads where there are lots
of concurrent lookup and writes? I really don't know (note that
"lookup" needs to be uncached and actually hit the lowlevel filesystem
for the locking to even trigger in the first place).
I guess some "concurrent readdir with unlink" load would show that
behavior, but is it _realistic_? No idea. Let's not worry about it too
much until somebody shows a reason to worry.
Linus
