[dm-crypt] multiple crypt devices not using multiple CPUs

Brian J. Murrell brian at interlinx.bc.ca
Sun Dec 16 23:02:18 CET 2012


On 12-12-16 04:25 PM, Milan Broz wrote:
> 
> In current kernels, work keeps on cpu which submitted it.

So a single process doing parallel reads from multiple devices (I'm sure
you could guess where I'm going with this) will never see more
throughput than it would from a single device?  If so, all the more
reason to get multi-core support (for a single process of course)
involved.  :-/

> Please read
> http://www.saout.de/pipermail/dm-crypt/2012-July/002582.html

Yeah.  I'm trying to see this "more processes" behavior but even the two
dds each running in different shells are still attacking the same core.

> (and try to run the second case with direct-io, iow add oflag=direct for dd)

oflag=direct?

# dd oflag=direct of=/dev/null if=/dev/mapper/t1-use bs=1M count=1000
dd: opening ‘/dev/null’: Invalid argument

I guess O_DIRECT it not valid for /dev/null.

Cheers,
b.


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