[lustre-discuss] Are there any performance hits with the https://access.redhat.com/security/vulnerabilities/speculativeexecution?

[Patrick Farrell]

Note though that since the servers live in kernel space they are also going to be affected only minimally.  The Lustre server code itself will see zero effect, since it’s entirely kernel code.  Other things running on those servers may see impact, and if there’s enough user space stuff, increased usage there could reduce resources available for Lustre.

Note also it’s important to distinguish here: the issue is not context switches (which is scheduling a different process), it’s syscalls, which do not require a context switch.  Context switches already had this sort of overhead.  A syscall is not a context switch.  (But the KPTI changes make the effective difference smaller.)


________________________________
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of E.S. Rosenberg <esr+lustre at mail.hebrew.edu>
Sent: Monday, January 8, 2018 7:05:48 AM
To: Arman Khalatyan
Cc: Lustre discussion
Subject: Re: [lustre-discuss] Are there any performance hits with the https://access.redhat.com/security/vulnerabilities/speculativeexecution?

The hit is mainly for things that do context switches (which IO is the biggest thing in.

On Mon, Jan 8, 2018 at 1:23 PM, Arman Khalatyan <arm2arm at gmail.com<mailto:arm2arm at gmail.com>> wrote:
Ok, We did some tests with the new lustre clients(no patch on servers)
I can confirm like Marek: maximum downgrade is about 40% by rsync with
small files, lfs find on large folders 45% performance penalty:(
We found terrible performance on the test system with zfs+compression+lustre.
Good news: the compute node flops are about 1% or even none. So only
IO intensive applications are impacted.

Cheers,
Arman.

On Mon, Jan 8, 2018 at 11:45 AM, Marek Magryś <m.magrys at cyfronet.pl<mailto:m.magrys at cyfronet.pl>> wrote:
> Hi all,
>
>> I wonder if any performance impacts on lustre with the new security
>> patches for the Intel?
>
> According to our initial tests on 3.10.0-693.11.6.el7.x86_64 kernel
> (Centos 7.4) with Lustre 2.10.2, there is a penalty of ca. 10% in nice
> workloads (1MB IO) up to 40% in 4k IOs. Tested with IOR.
>
> It looks bad, however probably we don't need to patch the servers, as
> Lustre lives in kernelspace anyway. Some kind of advisory from Intel
> HPDD would be nice here.
>
> Cheers,
> Marek
>
> --
> Marek Magrys
> ACC Cyfronet AGH-UST
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