Re: [PATCH] reorder struct files_struct

[Peter Staubach <staubach@redhat.com>]

Eric Dumazet wrote:

> Hi
>
> Browsing (and using) the excellent RCU infrastructure for files that 
> was adopted for 2.6.14-rc1, I noticed that the file_lock spinlock sit 
> close to mostly read fields of 'struct files_struct'
>
> In SMP (and NUMA) environnements, each time a thread wants to open or 
> close a file, it has to acquire the spinlock, thus invalidating the 
> cache line containing this spinlock on other CPUS. So other threads 
> doing read()/write()/... calls that use RCU to access the file table 
> are going to ask further memory (possibly NUMA) transactions to read 
> again this memory line.
>
> Please consider applying this patch. It moves the spinlock to another 
> cache line, so that concurrent threads can share the cache line 
> containing 'count' and 'fdt' fields. 


How was the performance impact of this change measured?

    Thanx...

       ps