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Re: virtiofs vs 9p performance(Re: tools/virtiofs: Multi threading seems


From: Christian Schoenebeck
Subject: Re: virtiofs vs 9p performance(Re: tools/virtiofs: Multi threading seems to hurt performance)
Date: Tue, 29 Sep 2020 15:59:34 +0200

On Dienstag, 29. September 2020 15:49:42 CEST Vivek Goyal wrote:
> > Depends on what's randomized. If read chunk size is randomized, then yes,
> > you would probably see less performance increase compared to a simple
> > 'cat foo.dat'.
> 
> We are using "fio" for testing and read chunk size is not being
> randomized. chunk size (block size) is fixed at 4K size for these tests.

Good to know, thanks!

> > If only the read position is randomized, but the read chunk size honors
> > iounit, a.k.a. stat's st_blksize (i.e. reading with the most efficient
> > block size advertised by 9P), then I would assume still seeing a
> > performance increase.
> 
> Yes, we are randomizing read position. But there is no notion of looking
> at st_blksize. Its fixed at 4K. (notice option --bs=4k in fio
> commandline).

Ah ok, then the results make sense.

With these block sizes you will indeed suffer a performance issue with 9p, due 
to several thread hops in Tread handling, which is due to be fixed.

Best regards,
Christian Schoenebeck





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