Re: [PATCH v6 0/7] vfs: Non-blockling buffered fs read (page cache only)

[Volker Lendecke <Volker.Lendecke@SerNet.DE>]

On Thu, Dec 04, 2014 at 03:11:02PM -0800, Andrew Morton wrote:
> I can see all that, but it's handwaving.  Yes, preadv2() will perform
> better in some circumstances than fincore+pread.  But how much better? 
> Enough to justify this approach, or not?
> 
> Alas, the only way to really settle that is to implement fincore() and
> to subject it to a decent amount of realistic quantitative testing.
> 
> Ho hum.
> 
> Could you please hunt down some libuv developers, see if we can solicit
> some quality input from them?  As I said, we really don't want to merge
> this then find that people don't use it for some reason, or that it
> needs changes.

All I can say from a Samba perspective is that none of the ARM based
Storage boxes I have seen so far do AIO because of the base footprint
for every read. For sequential reads kernel-level readahead could kick
in properly and we should be able to give them the best of both worlds:
No context switches in the default case but also good parallel behaviour
for other workloads.  The most important benchmark for those guys is to
read a DVD image, whether it makes sense or not.

Volker

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