linux-kernel - Re: Disable L1/L2/L3 cache and MTRR

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]

Message-ID: <AANLkTi=upG5Sw=shimWb12YST-XaJYdrYBJCOdTjp_vg@mail.gmail.com>
Date:	Thu, 21 Oct 2010 17:50:21 -0400
From:	Andev <debiandev@...il.com>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
Cc:	linux kernel <kernelnewbies@...linux.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Disable L1/L2/L3 cache and MTRR

On Thu, Oct 21, 2010 at 4:23 PM, Sitsofe Wheeler <sitsofe@...oo.com> wrote:

>> Now when I run some sample benchmarks they show a slowdown of almost 1000x!!
>>
>> This is not reasonable since the max. The slowdown I was expecting is 200x
>> considering that it will take 200 cycles to read from DRAM.
>
> Assuming the cache was completely disabled, won't the impact be
> cumulative? E.g. imagine a memory read takes one cycle from cache and
> 100 from main memory. If you read 5 instructions from cache that will
> take 5 cycles. If you read 5 instructions from main memory that will be
> 5*100 so 500 cycles. If it is 10 instructions then it is 10 vs 1000 and
> so on...
>
> Are you searching for an improvement in determinism?

Yes, if that was so, the slowdown is still 100x.

In my test case, I removed all the entries from /proc/mtrr and also
disabled L1/L2/L3 caches.
When I run a benchmark which runs for 4 sec with cache, it takes
almost 3000 secs without cache.

I think I am messing up the /proc/mtrr file.

Regards,
Andev.
--
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/