Re: [RFC,PATCH 4/14] knfsd: has_wspace per transport

[Chuck Lever <chuck.lever@oracle.com>]

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Greg Banks wrote:
> On Wed, May 23, 2007 at 09:36:55AM -0400, Chuck Lever wrote:
>> Greg Banks wrote:
>>> On Wed, May 23, 2007 at 12:22:44AM -0500, Tom Tucker wrote:
>>>>
>>>> On 5/22/07 9:32 PM, "Greg Banks" <gnb@sgi.com> wrote:
>>>>
>>>>> On Tue, May 22, 2007 at 12:34:23PM -0500, Tom Tucker wrote:
>>>> I need to do a little clean up (e.g. atomic_inc()) and then I'll add them 
>>>> as
>>>> suggested. If there are dissenters, please speak now...
>>> You should be able to get away with just ++.  They're only stats,
>>> it's not like you have logic depending on them being exact.
>> The usual way to do this is to allocate separate stat arrays for each 
>> CPU.  All the per-CPU arrays are summed only when something wants to 
>> display stat totals.
>>
>> That way you can use ++, be fairly sure you will get accurate 
>> statistics, and not have to be concerned about CPU cache effects or lock 
>> contention.
> 
> Here in SGI, home of the multiple-thousand CPU Linux boxes, making
> data structures per-cpu tends to be done...thoughtfully.
> 
> In any case, the remainder of svc_stat gets no such treatment today.

I based the new NFS client stats on what was done by the networking 
layer, which uses the per-CPU pattern.  I was under the impression that 
methodology was preferred for adding new stat keeping.  But I'm aware 
that the existing NFS client and server stat keeping infrastructure uses 
just a simple array for each RPC program/version.

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