[OpenAFS-devel] read performance 1.5.74 Linux

[Steve Simmons]

On May 12, 2010, at 10:48 AM, Jeffrey Altman wrote:

> On 5/11/2010 1:01 PM, Hartmut Reuter wrote:
>>=20
>> I have now ported AFS/RXOSD to 1.5.74.
>> I am testing the client against servers running 1.4.12-osd.
>>=20
>> My client configuration is memcache with chunksize 18 (256K).
>> Writing to the fileserver and also to the rxosd is as fast as with =
the 1.4.12
>> client (I am testing on my laptop with the whole test-cell in the =
laptop, so 30
>> MB/s is already an acceptable value).
>>=20
>> But reading large files is terribly slow (~ 1 MB/s). With the 1.4.12 =
client read
>> and write have about the same speed.
>>=20
>> with rxdebug -peer -long I can also see that some times in the rtt =
the
>> fileserver or rxosd see is growing up to several seconds and then =
again going
>> down to a ms. So there seems to be something strange in the rx-layer.
>> It also shows a lot of resends (about 1 %).
>>=20
>> Any idea?
>>=20
>> Hartmut
>=20
> The first thing that comes to mind is that we found the rx library was
> dropping packets on the floor under high load.  This was fixed in the
> 1.5.74 release but has not been fixed in the 1.4.12 release.

Any feel for the net effect on throughput? Is the improvement =
significant enough to consider backporting to 1.4.13?

> The 1.5.74 client should be able to put more load on the file server
> as it does a much better job of efficiently reading from the page
> cache.

I don't understand the connection here. Hartmut seems to be saying that =
a 1.4.12osd client reading from a 1.4.12osd server runs 30x faster than =
a 1.5.74osd client reading from a 1.4.12osd server. Improvements in =
1.5.74 client-side reading of the page cache shouldn't have any affect - =
presumably one is only reading the file because it isn't in page or disk =
cache. 30-fold is a pretty big number, too.

Steve