netdev - Re: [PATCH] improved locking performance in rt_run

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Date:	Sun, 20 May 2007 15:11:48 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	davem@...emloft.net (David Miller)
Cc:	djohnson+linux-kernel@...starentnetworks.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] improved locking performance in rt_run_flush()

David Miller <davem@...emloft.net> wrote:
> From: Dave Johnson <djohnson+linux-kernel@...starentnetworks.com>
>> 
>> The below patch changes rt_run_flush() to only take each spinlock
>> protecting the rt_hash_table once instead of taking a spinlock for
>> every hash table bucket (and ending up taking the same small set 
>> of locks over and over).

...

> I'm not ignoring it I'm just trying to brainstorm whether there
> is a better way to resolve this inefficiency. :-)

The main problem I see with this is having to walk and free each
chain with the lock held.  We could avoid this if we had a pointer
in struct rtable to chain them up for freeing later.

I just checked and struct rtable is 236 bytes long on 32-bit but
the slab cache pads it to 256 bytes so we've got some free space.
I suspect 64-bit should be similar.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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