From: Eric Dumazet <dada1@cosmosbay.com>
To: Stephen Hemminger <shemminger@osdl.org>
Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org
Subject: Re: [PATCH] convert hh_lock to seqlock
Date: Thu, 07 Dec 2006 23:27:00 +0100 [thread overview]
Message-ID: <45789534.1050703@cosmosbay.com> (raw)
In-Reply-To: <20061207131553.45e4388b@localhost>
Stephen Hemminger a écrit :
> On Thu, 07 Dec 2006 21:23:07 +0100
> Eric Dumazet <dada1@cosmosbay.com> wrote:
>
>> Stephen Hemminger a écrit :
>>> The hard header cache is in the main output path, so using
>>> seqlock instead of reader/writer lock should reduce overhead.
>>>
>> Nice work Stephen, I am very interested.
>>
>> Did you benchmarked it ?
>>
>> I ask because I think hh_refcnt frequent changes may defeat the gain you want
>> (ie avoiding cache line ping pongs between cpus). seqlock are definitly better
>> than rwlock, but if we really keep cache lines shared.
>>
>> So I would suggest reordering fields of hh_cache and adding one
>> ____cacheline_aligned_in_smp to keep hh_refcnt in another cache line.
>>
>> (hh_len, hh_lock and hh_data should be placed on a 'mostly read' cache line)
>>
>> Thank you
>> Eric
>
> It doesn't make any visible performance difference for real networks;
> copies and device issues are much larger.
Hum, so 'my' machines must be unreal :)
>
> The hh_refcnt is used only when creating destroying neighbor entries,
> so except under DoS attack it doesn't make a lot of difference.
> The hh_lock is used on each packet sent.
Some machines create/delete 10.000 entries per second in rt_cache.
I believe they are real. DoS ? you tell it, some people wont agree.
# grep eth0 /proc/net/rt_cache|head -n 10000|cut -f13|sort -u|wc -l
359
(13th field of /proc/net/rt_cache is HHRef)
# rtstat -c1000 -i1
rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|rt_cache|
entries| in_hit|in_slow_|in_slow_|in_no_ro| in_brd|in_marti|in_marti|
out_hit|out_slow|out_slow|gc_total|gc_ignor|gc_goal_|gc_dst_o|in_hlist|out_hlis|
| | tot| mc| ute| | an_dst| an_src|
| _tot| _mc| | ed| miss| verflow| _search|t_search|
2467048|2479640328|1334812199| 0| 0| 34| 0|
117112|6139056109|7510556324| 0| 0| 0| 0|
0|8864696485|9819074477|
2465642| 16594| 4791| 0| 0| 0| 0| 0|
2387| 2738| 0| 0| 0| 0| 0| 21878| 7478|
2464482| 16505| 4765| 0| 0| 0| 0| 0|
2460| 2669| 0| 0| 0| 0| 0| 22224| 7499|
2463512| 17281| 4640| 0| 0| 0| 0| 0|
2449| 2632| 0| 0| 0| 0| 0| 22069| 7240|
2462651| 16504| 4314| 0| 0| 0| 0| 0|
2446| 2497| 0| 0| 0| 0| 0| 20796| 6979|
2462175| 18152| 5792| 0| 0| 0| 0| 0|
2448| 2791| 0| 0| 0| 0| 0| 26164| 7731|
2461889| 16970| 5059| 0| 0| 0| 0| 0|
2535| 2829| 0| 0| 0| 0| 0| 22614| 7595|
2461719| 16446| 4643| 0| 0| 0| 0| 0|
2496| 2717| 0| 0| 0| 0| 0| 21347| 7354|
2461775| 17098| 4782| 0| 0| 0| 0| 0|
2386| 2570| 0| 0| 0| 0| 0| 22448| 7049|
Thank you
Eric
next prev parent reply other threads:[~2006-12-07 22:26 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-07 19:33 [PATCH] convert hh_lock to seqlock Stephen Hemminger
2006-12-07 20:23 ` Eric Dumazet
2006-12-07 21:15 ` Stephen Hemminger
2006-12-07 22:27 ` Eric Dumazet [this message]
2006-12-07 22:53 ` Stephen Hemminger
2006-12-07 23:02 ` Eric Dumazet
2006-12-07 23:07 ` David Miller
2006-12-08 8:06 ` [PATCH] NET : force a cache line split in hh_cache in SMP Eric Dumazet
2006-12-08 8:08 ` David Miller
2006-12-07 23:08 ` [PATCH] convert hh_lock to seqlock David Miller
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