Re: Lockless page cache test results

[Nick Piggin]

Andrew Morton wrote:

> > The top of the 4-client
> > vanilla run profile looks like this:
> >
> > samples  %        symbol name
> > 65328    47.8972  find_get_page
> >
> > Basically the machine is fully pegged, about 7% idle time.
>
>
> Most of the time an acquisition of tree_lock is associated with a disk
> read, or a page-size memset, or a page-size memcpy.  And often an
> acquisition of tree_lock is associated with multiple pages, not just a
> single page.

Still, most of the times it is acquired would be once per page for
read, write, nopage.

For read and write, often it will be a full page memcpy but even such
a memcpy operation can quickly become insignificant compared to tl
contention.

Anyway, whatever. What needs to be demonstrated are real world
improvements at the end of the day.

> So although the graph looks good, I wouldn't view this as a super-strong
> argument in favour of lockless pagecache.

No. Cool numbers though ;)

--
SUSE Labs, Novell Inc.

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