Re: [Virtio-fs] [PATCH 1/1] virtiofsd: Do not use a thread pool by default

[Vivek Goyal]

On Tue, Feb 16, 2021 at 05:55:26PM +0000, Dr. David Alan Gilbert wrote:
> * Vivek Goyal (vgoyal@redhat.com) wrote:
> > Currently we created a thread pool (With 64 max threads per pool) for
> > each virtqueue. We hoped that this will provide us with better scalability
> > and performance.
> > 
> > But in practice, we are getting better numbers in most of the cases
> > when we don't create a thread pool at all and a single thread per
> > virtqueue receives the request and processes it.
> > 
> > Hence, I am proposing that we switch to no thread pool by default
> > (equivalent of --thread-pool-size=0). This will provide out of
> > box better performance to most of the users. In fact other users
> > have confirmed that not using a thread pool gives them better
> > numbers. So why not use this as default. It can be changed when
> > somebody can fix the issues with thread pool performance.
> > 
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> 
> OK, lets try it - I still worry it really means we're missing something
> silly about them, you'd really think eventually the threads should help.

Agreed. Once we figure out what are we missing with threading and
start getting better performance with multi-threading, we will need
to make thread pool default again.

Vivek
> 
> 
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> > ---
> >  tools/virtiofsd/fuse_lowlevel.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/virtiofsd/fuse_lowlevel.c 
> > b/tools/virtiofsd/fuse_lowlevel.c
> > index e94b71110b..fbdf62ee9b 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.c
> > +++ b/tools/virtiofsd/fuse_lowlevel.c
> > @@ -18,7 +18,7 @@
> >  
> >  #include <sys/file.h>
> >  
> > -#define THREAD_POOL_SIZE 64
> > +#define THREAD_POOL_SIZE 0
> >  
> >  #define OFFSET_MAX 0x7fffffffffffffffLL
> >  
> > -- 
> > 2.25.4
> -- 
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
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