Re: Btrfs v0.16 released

[tvrtko.ursulin@sophos.com]

Chris Mason wrote on 07/08/2008 11:34:02:

> > > * Helper threads for checksumming and other background tasks.  Most 
CPU
> > > intensive operations have been pushed off to helper threads to take
> > > advantage of SMP machines.  Streaming read and write throughput now
> > > scale to disk speed even with checksumming on.
> > 
> > Can this lead to the same Priority Inversion issues as seen with
> > kjournald?
> 
> Yes, although in general only the helper threads end up actually doing
> the IO for writes.  Unfortunately, they are almost but not quite an
> elevator.  It is tempting to try sorting the bios on the helper queues
> etc.  But I haven't done that because it gets into starvation and other
> fun.
> 
> I haven't done any real single cpu testing, it may make sense in those
> workloads to checksum and submit directly in the calling context.  But
> real single cpu boxes are harder to come by these days.

[just jumping in as a casual bystander with one remark]

For this purpose it seems booting up with limiting to one CPU should be 
sufficient.

Tvrtko


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