[dm-crypt] slow read performance, but fast writes?

Peter Merhaut petermerhaut at gmail.com
Thu Sep 15 13:07:46 CEST 2011


Yeah but why is it using one cpu for encryption? I got 6 encrypted block
devices. When writing to them, all cpu cores are used for encryption,
therefor it's fast. When reading, it seems to use 1 cpu for all 6 crypto
threads?

Am 09/15/2011 12:45 PM, schrieb Milan Broz:
> On 09/15/2011 11:49 AM, Nikolay Kichukov wrote:
>> Hi,
>> this query is best suited for md-raid mailing list as what you measure:
>>
>> dd if=/dev/md3 of=/dev/null bs=1M
>>
>> does not involve any decryption. You are reading directly from the md device and there is no matter what is actually there.
> heh. I read that as crypt device and it is MD directly, sorry for confusion.
> Seems my brain is still in different timezone :)
>
> yes, this test has nothing to do with crypt.
>
> Anyway, it is interesting that the problem is there even without crypt,
> perhaps you should ask on linux-raid list then.
>
> for badblock - I guess it just submits all IO from one cpu,
> so only one core is used for encryption in fact. There applies the same what I wrote before.
>
> Milan



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