cvs commit: src/sys/dev/streams streams.csrc/sys/kernkern_descrip.csrc/sys/opencrypto cryptodev.c

[Scott Long]

On Mon, 20 Oct 2003, Alan Cox wrote:
> On Mon, Oct 20, 2003 at 01:58:08PM -0600, Scott Long wrote:
> > On Mon, 20 Oct 2003, Scott Long wrote:
> > >
> > >
> > > On Mon, 20 Oct 2003, Scott Long wrote:
> > >
> > > > On Mon, 20 Oct 2003, David Malone wrote:
> > > > > > > This reminds me that we still hold Giant around pipe(2) because it isn't
> > > > > > > declared MPSAFE in the syscall table.  Is this still necessary?
> > > > >
> > > > > > I've been suspicious of this too, and I was hoping that you would have
> > > > > > an answer.  Can we go ahead and correct this?
> > > > >
> > > > > I think we may need to check the calling of pipeclose() in pipe(),
> > > > > but as this is only done in an error case, it is probably safe enough
> > > > > to just grab Giant for that. (The mac_* calls may need to be checked
> > > > > too).
> > > >
> > > > pipeclose() seems to have some concept of locking, though I don't know
> > > > what the implications are of it saying, 'gee, the mutex on this pipe was
> > > > never initialized, so I just won't worry about locking.'  Towards the
> > > > end of pipeclose() Giant is acquired, though that action is likely no
> > > > longer needed either.
> > >
> > > Nix that last part, I was looking at a stale file.  pipeclose() does not
> > > explicitely grab Gaint.
> > >
> > > Scott
> > >
> > >
> >
> > I've run several buildworlds while doing background pipe tests, all
> > without any problems with WITNESS and INVARIANTS enabled on a fast SMP
> > machine.  I can't report any performance change since I'm only testing
> > correctness now, but it looks promising.  I'd advise to go ahead and
> > throw the switch on this.
> >
>
> This only changes the creation of pipes.  Thus, I wouldn't expect
> an observable difference.
>
> I believe that the actual use of pipes has been free of Giant
> for some time.  (In truth, there is a small bit of pmap-level
> code that still acquires Giant.)
>
> Alan
>
>

Right, it looks like pipe_read() and pipe_write() both run without Giant.
However, in an environment like 'make -j4 buildworld' on SMP, it seems
to help with Giant contention a little bit.


Scott