lkml.org 
[lkml]   [2016]   [Feb]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3] net:Add sysctl_max_skb_frags
From
Date
On 03.02.2016 13:20, Herbert Xu wrote:
> On Wed, Feb 03, 2016 at 12:36:21PM +0100, Hannes Frederic Sowa wrote:
>>
>> Agreed that it feels like a hack, but a rather simple one. I would
>> consider this to be just a performance improvement. We certainly need
>> a slow-path when virtio drivers submit gso packets to the stack (and
>> already discussed with Hans). The sysctl can't help here. But without
>> the sysctl the packets would constantly hit the slow-path in case of
>> e.g. IPoIB and that would also be rather bad.
>
> So you want to penalise every NIC in the system if just one of
> them is broken? This is insane. Just do the partial linearisation
> in that one driver that needs it and not only won't you have to
> penalise anyone else but you still get the best result for that
> driver that needs it.

Most normal Ethernet systems and drivers currently don't need tweating
this knob at all, only some special kinds of installations. This patch
referred to IPoIB as a possible user which drivers/firmware/cards seem
to have this problem. Current behavior just leaves everything as-is.

If you use IPoIB you probably use it quite regular and linearizing an
skbs *always* seems to be much more work than simply capping the number
of frags globally.

> Besides, you have to implement the linearisation anyway because
> of virtualisation.

Yes, the slow-path is necessary. But instead of writing a new
complicated linearizing function to just reduce the fragments we could
also simply linearize it completely and ask the admin to also tune the
vm guests.

I only see this tuning in kind in very specific environments where the
admins now what they do.

Bye,
Hannes

\
 
 \ /
  Last update: 2016-02-03 15:21    [W:0.134 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site