linux-kernel - Re: Big I/O latencies, except when iotop is hooked

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Mon, 14 May 2012 11:08:22 +0200
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Big I/O latencies, except when iotop is hooked

Hi,

On Mon, May 14, 2012 at 10:59 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 10 May 2012, Arnd Bergmann wrote:
>> 176 is extremely bad, yes. A good value would be between 1 and 3.
>> The algorithm is probably not 'la' but 'dl' and the page size (-b)
>> could be smaller -- you have to test by passing '--blocksize=1024' to
>> the --open-au test and see where it starts getting drastically
>> smaller (if 4KB gives you about half the throughput of 8KB,
>> 8KB is the page size). Those two can make the result better.
>>
>> As I said, the erase block size is more likely to be 4MB, which
>> will make the flashsim result worse.
>>
>> Does flashsim give a better number for a trace taken with iotop
>> running?
>>
>> Can you send me or upload that iolog file?
>
> Hi Felipe,
>
> Any update?

Nope, sorry, my laptop got fried. I have a new one and I might be able
to test later today, I don't see why I would have any problems
reproducing this there, but lets see.

> I'd really be interested in the trace file so that we
> can look at data of a real-world case that hurts. I've discussed
> your problem in the Linaro storage team meeting, and the question
> came up whether this only happens with encryption enabled.

As I already said, this also happens without encryption.

> Which kind of encryption method do you actually use? Depending
> on how the encryption is implemented, two things could possibly
> go wrong that would not happen without it:

I just do 'cryptsetup luksFormat' I'm not sure what is their default.
According to the manpage it's aes-cbc-essiv:sha256. I tried with
different --align-payload values, but none that actually improved the
situation.

Anyway, the problem is visible even with plain ext4.

Cheers.

-- 
Felipe Contreras
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/