Re: [Xen-devel] [PATCH] Reduce overhead in find_domain_by_id() [0/2]

[Keir Fraser <keir@xxxxxxxxxxxxx>]

Okay, sounds good. I don't want the whole Linux RCU mechanism in Xen
particularly. Linux may well need the complexity because it leans on RCU
quite heavily these days, but Xen will do so a whole lot less I'm sure and
something much simpler should suffice. I'll look into this -- the patches
you sent provide a good starting point, thanks!

 -- Keir

On 6/12/06 11:52, "Apparao, Padmashree K" <padmashree.k.apparao@xxxxxxxxx>
wrote:

> Keir,
> 
> Earlier this summer I had done some experiments with Iperf and found
> that find_domain_id was consuming 7% of cpu while do_grant_table_op was
> consuming 10.5%. A quick fix to figure what the upper bound of
> performance gain was to remove the hash table lookups in
> find_domain_by_id and we saw a 12% improvement in perf receive
> performance.
> The results of these finding were published in our paper at VTDC.
> In that paper we also discuss how the inter vm communication by grant
> tables was consuming a considerable amount of time and what could be
> possibly done to optimize.
> 
> I will send the paper is a separate note to you and Renato.
> 
> Thanks
> - Padma
> 
> 
> 
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
> Sent: Wednesday, December 06, 2006 12:44 AM
> To: Santos, Jose Renato G; xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: Yoshio Turner; Jose Renato Santos; G John Janakiraman
> Subject: Re: [Xen-devel] [PATCH] Reduce overhead in find_domain_by_id()
> [0/2]
> 
> On 6/12/06 1:35 am, "Santos, Jose Renato G" <joserenato.santos@xxxxxx>
> wrote:
> 
>> 
>> This is a set of patches to improve performance of
> find_domain_by_id().
>> find_domain_by_id shows up high in profiles for network I/O intensive
>> workloads.
>> Most of the cost for this function comes from 3 main functions (of
>> aproximate equal costs): 1)read_lock(), 2)read_unlock() and
>> 3)get_domain().
>> These patches replace the lock used for accessing domain_list and
>> domain_hash with a lock free RCU scheme. Experiments confirm that the
>> cost of find_domain_by_id() is in fact reduced by 2/3.
>> The patches apply cleanly to changeset 12732.
> 
> Do you have numbers for performance improvement on a macro benchmark?
> 
>  -- Keir
> 
> 
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