Re: [PATCH] Mantaining turnstile aligned to 128 bytes in i386 CPUs

On Tuesday 16 January 2007 15:36, Attilio Rao wrote:
> 2007/1/16, John Baldwin <jhb_at_freebsd.org>:
> > On Tuesday 16 January 2007 11:51, Attilio Rao wrote:
> > > 2006/7/28, Attilio Rao <attilio_at_freebsd.org>:
> > > >
> > > > After some thinking, I think it's better using init/fini methods
> > > > (since they hide the sizeof(struct turnstile) with size parameter).
> > > >
> > > > Feedbacks and comments are welcome:
> > > > http://users.gufi.org/~rookie/works/patches/uma_sync_init.diff
> > >
> > > [CC'ed all the interested people]
> > >
> > > Even if a long time is passed I did some benchmarks based on ebizzy 
tool.
> > > This program claims to reproduce a real httpd server behaviour and is
> > > used into the Linux world for benchmarks, AFAIK.
> > > I think that results of the comparison on this patch is very
> > > interesting, and I think it worths a commit :)
> > > I think that results can be even better on a Xeon machine (I had no
> > > chance to reproduce this on some of these).
> > > (Results taken in consideration have been measured after some starts,
> > > in order to minimize caching differences).
> > >
> > > The patch:
> > > http://users.gufi.org/~rookie/works/patches/ts-sq/ts-sq.diff
> >
> > Looks good.  Some minor nits are that in subr_turnstile.c in the comment I
> > would say "a turnstile is allocated" rather than "a turnstile is got from 
a
> > specific UMA zone" as it reads a little bit clearer.  Also, I would
> > say "Allocate a" rather than "Get a" for the two _alloc() functions.  
Also,
> > why not just use UMA_ALIGN_CACHE and make UMA_ALIGN_CACHE (128 - 1) on 
i386
> > and amd64 rather than adding a new UMA_ALIGN_SYNC?
> 
> I was thinking that in this way anyone who wants to replace the
> syncronizing primitive boundary to an appropriate value can do it.
> I just used UMA_ALIGN_CACHE as default value beacause I don't know the
> better boundary (for syncronizing primitives) for other arches.

Is there a good reason to not cache-align synch primitives?  That is, why 
would an arch not use cache-align?  Also, is there a reason to not update 
UMA_ALIGN_CACHE on x86?

-- 
John Baldwin