netdev - Re: [PATCH nf-next-2.6] xt_hashlimit: RCU conversion

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Date:	Thu, 01 Apr 2010 14:36:54 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jorrit Kronjee <j.kronjee@...opact.nl>,
	netfilter-devel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH nf-next-2.6] xt_hashlimit: RCU conversion

Eric Dumazet wrote:
> Le jeudi 01 avril 2010 à 13:03 +0200, Patrick McHardy a écrit :
>>> -/* allocate dsthash_ent, initialize dst, put in htable and lock it */
>>> -static struct dsthash_ent *
>>> -dsthash_alloc_init(struct xt_hashlimit_htable *ht,
>>> -		   const struct dsthash_dst *dst)
>> Is there a reason for moving this function downwards in the file?
>> That unnecessarily increases the diff and makes the patch harder to
>> review. For review purposes I moved it back up, resulting in 42
>> lines less diff.
>> --
> 
> Well, this is because I had to move inside this function various
> initializations and these inits use user2credits() which was defined
> after dsthash_alloc_init().

I thought I also tried to compile it after my change, but apparently
I made some mistake :)

> But we can avoid this since we hold the entry spinlock, and before hash
> insertion.
> 
> Only the lookup fields and the spinlock MUST be committed to memory
> before the insert. Other fields can be initialized later by caller.
> 
> Here is V2 of patch, I added locking as well in dl_seq_real_show()
> because we call rateinfo_recalc(). htable main lock doesnt anymore
> protects each entry rateinfo.
> 
> Thanks
> 
> [PATCH nf-next-2.6] xt_hashlimit: RCU conversion
> 
> xt_hashlimit uses a central lock per hash table and suffers from
> contention on some workloads. (Multiqueue NIC or if RPS is enabled)
> 
> After RCU conversion, central lock is only used when a writer wants to
> add or delete an entry.
> 
> For 'readers', updating an existing entry, they use an individual lock
> per entry.

Applied, thanks a lot Eric.
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