Re: Question about socket timeouts

On Monday, August 26, 2013 2:23:44 pm Davide Italiano wrote:
> On Fri, Aug 23, 2013 at 5:29 PM, John Baldwin <jhb_at_freebsd.org> wrote:
> > On Friday, August 23, 2013 9:53:12 am Davide Italiano wrote:
> >> On Fri, Aug 23, 2013 at 3:45 PM, John Baldwin <jhb_at_freebsd.org> wrote:
> >> > On Friday, August 23, 2013 2:27:58 am Vitja Makarov wrote:
> >> >> 2013/8/22 John Baldwin <jhb_at_freebsd.org>:
> >> >> > On Thursday, August 22, 2013 12:18:48 am Vitja Makarov wrote:
> >> >> >> 2013/8/21 John Baldwin <jhb_at_freebsd.org>:
> >> >> >> > On Monday, August 19, 2013 11:13:02 pm Daniel Eischen wrote:
> >> >> >> >> On Mon, 19 Aug 2013, Adrian Chadd wrote:
> >> >> >> >>
> >> >> >> >> > Yes! Please file a PR!
> >> >> >> >>
> >> >> >> >> This sorta implies that both are acceptable (although,
> >> >> >> >> the Linux behavior seems more desirable).
> >> >> >> >>
> >> >> >> >>    http://austingroupbugs.net/view.php?id=369
> >> >> >> >
> >> >> >> > No, that says "round up", so it does mean that the requested 
timeout
> >> >> >> > should be the minimum amount slept.  tvtohz() does this.  Really 
odd
> >> >> >> > that the socket code is using its own version of this rather than
> >> >> >> > tvtohz().
> >> >> >> >
> >> >> >> > Oh, I bet this just predates tvtohz().  Interesting that it keeps
> > getting
> >> >> >> > bug fixes in its history that simply using tvtohz() would have
> > solved.
> >> >> >> >
> >> >> >> > Try this:
> >> >> >> >
> >> >> >> > Index: uipc_socket.c
> >> >> >> > 
===================================================================
> >> >> >> > --- uipc_socket.c       (revision 254570)
> >> >> >> > +++ uipc_socket.c       (working copy)
> >> >> >> > _at__at_ -2699,21 +2699,16 _at__at_ sosetopt(struct socket *so, struct 
sockopt
> > *sopt)
> >> >> >> >                         if (error)
> >> >> >> >                                 goto bad;
> >> >> >> >
> >> >> >> > -                       /* assert(hz > 0); */
> >> >> >> >                         if (tv.tv_sec < 0 || tv.tv_sec > INT_MAX 
/
> > hz ||
> >> >> >> >                             tv.tv_usec < 0 || tv.tv_usec >= 
1000000)
> > {
> >> >> >> >                                 error = EDOM;
> >> >> >> >                                 goto bad;
> >> >> >> >                         }
> >> >> >> > -                       /* assert(tick > 0); */
> >> >> >> > -                       /* assert(ULONG_MAX - INT_MAX >= 
1000000);
> > */
> >> >> >> > -                       val = (u_long)(tv.tv_sec * hz) + 
tv.tv_usec
> > / tick;
> >> >> >> > -                       if (val > INT_MAX) {
> >> >> >> > +                       val = tvtohz(&tv);
> >> >> >> > +                       if (val == INT_MAX) {
> >> >> >> >                                 error = EDOM;
> >> >> >> >                                 goto bad;
> >> >> >> >                         }
> >> >> >> > -                       if (val == 0 && tv.tv_usec != 0)
> >> >> >> > -                               val = 1;
> >> >> >> >
> >> >> >> >                         switch (sopt->sopt_name) {
> >> >> >> >                         case SO_SNDTIMEO:
> >> >> >> >
> >> >> >>
> >> >> >> That must help. But I want to see the issue solved in the next
> >> >> >> release. I can't apply patch to the production system. Btw in
> >> >> >> production environment we have kern.hz set to 1000 so it's not a
> >> >> >> problem there.
> >> >> >
> >> >> > Can you test this in some way in a test environment?
> >> >> >
> >> >>
> >> >> Ok, sorry for posting out of the list.
> >> >>
> >> >> Simple test program is attached. Without your patch timeout expires in
> >> >> about 20ms. With it it's ~40ms.
> >> >>
> >> >> 40 instead of 30 is beacuse of odd tick added by tvtohz().
> >> >
> >> > Ok, thanks.  tvtohz() will be good to MFC (and I will do that), but for
> >> > HEAD I think we can fix this to use a precise timeout.  I've cc'd 
davide_at_
> >> > so he can take a look at that.
> >> >
> >> > --
> >> > John Baldwin
> >>
> >> Hi,
> >> I think I can switch this code to new timeout KPI, but this will
> >> require the timeout field of 'struct sockbuf' to be changed from 'int'
> >> to 'sbintime_t' which breaks binary compatibility. Do you have any
> >> strong objections about this? If any, I would like this to happen ABI
> >> freeze, so it looks like this is the right moment.
> >
> > This should be fine to change now, it just can't be MFC'd (which we can't
> > do anyway).
> >
> > --
> > John Baldwin
> 
> Please consider the following patch:
> http://people.freebsd.org/~davide/review/socket_timeout.diff
> I've tested it and it works OK. I got a timeout which is ~= 25ms using
> the testcase provided by the user.
> The only doubt I have is about the range check, I've changed a bit
> because the 'integer' part of sbintime_t fits in 32-bits, but I'm not
> sure it's the best way of doing this.

Nice!  Bruce actually wants me to adjust the range check a bit (which will
fit in well with your changes I think).  Please let me get that fix in
(so it can be part of the future MFC) and then you can commit this.  Thanks!

Actually, I think you still need to patch the sogetopt() case to work correctly
(it is still doing a manual conversion from 'val' to a timeval assuming it is
in 'hz' units).

-- 
John Baldwin