Re: [patch 0/3] j_state_lock, j_list_lock, remove-bitlocks

[Andrew Morton]

Ingo Molnar <mingo@xxxxxxx> wrote:
>
> 
> * Andrew Morton <akpm@xxxxxxxx> wrote:
> 
> > I forget how much of the 1000% came from that, but it was quite a lot.
> > 
> > Removing the BKL was the first step.  That took the context switch
> > rate under high load from ~10,000/sec up to ~300,000/sec.  Because the
> > first thing a CPU hit on entry to the fs was then a semaphore. 
> > Performance rather took a dive.
> > 
> > Of course the locks also became much finer-grained, so the contention
> > opportunities lessened.  But j_list_lock and j_state_lock have fs-wide
> > scope, so I'd expect the context switch rate to go up quite a lot
> > again.
> > 
> > The hold times are short, and a context switch hurts rather ore than a
> > quick spin.
> 
> which particular workload was this - dbench? (I can try PREEMPT_RT on an
> 8-way, such effects will show up tenfold.)
> 

Oh gee, that was back in the days when Martin was being useful.  SDET, I
think.

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