Alex Williamson
2007-May-08 22:26 UTC
[Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
Is the patch below, that''s currently in the Xen tree, still
necessary? The original commit comment indicates this is so things like
''top'' don''t get upset during CPU hotplugs. But
should that be handled
by the hotplug infrastructure in the kernel (or top itself)? IMHO, this
breaks top more than fixes it. Now when I try to look at individual
processor statistics, I see quite a few lines of zeros (2 online CPUs,
16 possible CPUs). AFAICT, this also breaks all of the NPROCESSORS
queries for sysconf. Can we dump it? Thanks,
Alex
diff -pruN ../orig-linux-2.6.18/fs/proc/proc_misc.c ./fs/proc/proc_misc.c
--- ../orig-linux-2.6.18/fs/proc/proc_misc.c 2006-09-20 04:42:06.000000000
+0100
+++ ./fs/proc/proc_misc.c 2007-01-12 18:18:36.000000000 +0000
@@ -471,7 +471,7 @@ static int show_stat(struct seq_file *p,
(unsigned long long)cputime64_to_clock_t(irq),
(unsigned long long)cputime64_to_clock_t(softirq),
(unsigned long long)cputime64_to_clock_t(steal));
- for_each_online_cpu(i) {
+ for_each_possible_cpu(i) {
/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
user = kstat_cpu(i).cpustat.user;
--
Alex Williamson HP Open Source & Linux Org.
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Keir Fraser
2007-May-09 07:05 UTC
Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
On 8/5/07 23:26, "Alex Williamson" <alex.williamson@hp.com> wrote:> Is the patch below, that''s currently in the Xen tree, still > necessary? The original commit comment indicates this is so things like > ''top'' don''t get upset during CPU hotplugs. But should that be handled > by the hotplug infrastructure in the kernel (or top itself)?It has to be handled in top itself. With some versions at least it was the case that top would crash when CPUs where hot-unplugged. If you revert that patch, does your version of top work okay in the hot-unplug case (you have to run top across the unplug operation to see if it will crash or not)? -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Dave Lively
2007-May-09 13:52 UTC
Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
I made ''top'' deal with CPU hotplug a couple years ago, and submitted the changes to the ''procps'' maintainers, who never got back to me. I''ve given the patch to a number of external folks (in particular, some from the OSDL hotplug SIG), so it may have found its way into some versions of ''top''. In any case, I''ll try to track down the current status and dig up those patches Real Soon Now. Dave Lively Virtual Iron On 5/9/07, Keir Fraser <Keir.Fraser@cl.cam.ac.uk> wrote:> On 8/5/07 23:26, "Alex Williamson" <alex.williamson@hp.com> wrote: > > > Is the patch below, that''s currently in the Xen tree, still > > necessary? The original commit comment indicates this is so things like > > ''top'' don''t get upset during CPU hotplugs. But should that be handled > > by the hotplug infrastructure in the kernel (or top itself)? > > It has to be handled in top itself. With some versions at least it was the > case that top would crash when CPUs where hot-unplugged. If you revert that > patch, does your version of top work okay in the hot-unplug case (you have > to run top across the unplug operation to see if it will crash or not)? > > -- Keir > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Alex Williamson
2007-May-09 15:07 UTC
Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
On Wed, 2007-05-09 at 08:05 +0100, Keir Fraser wrote:> On 8/5/07 23:26, "Alex Williamson" <alex.williamson@hp.com> wrote: > > > Is the patch below, that''s currently in the Xen tree, still > > necessary? The original commit comment indicates this is so things like > > ''top'' don''t get upset during CPU hotplugs. But should that be handled > > by the hotplug infrastructure in the kernel (or top itself)? > > It has to be handled in top itself. With some versions at least it was the > case that top would crash when CPUs where hot-unplugged. If you revert that > patch, does your version of top work okay in the hot-unplug case (you have > to run top across the unplug operation to see if it will crash or not)?Top still crashes without that patch, but the patch just hides the problem. Top also crashes during a CPU hotplug operation on bare metal. I think this patch causes more problems than if fixes. Thanks, Alex -- Alex Williamson HP Open Source & Linux Org. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-May-09 15:32 UTC
Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
On 9/5/07 16:07, "Alex Williamson" <alex.williamson@hp.com> wrote:>> It has to be handled in top itself. With some versions at least it was the >> case that top would crash when CPUs where hot-unplugged. If you revert that >> patch, does your version of top work okay in the hot-unplug case (you have >> to run top across the unplug operation to see if it will crash or not)? > > Top still crashes without that patch, but the patch just hides the > problem. Top also crashes during a CPU hotplug operation on bare metal. > I think this patch causes more problems than if fixes. Thanks,The fact that physical CPU hotplug is an incredibly rare operation, even on the 0.001% of all systems that it is actually supported on, compared with virtual CPU hotplug being potentially quite frequent, is a real concern. Users are actually moderately likely to see this bug when running on Xen. In fact they used to, and then they complained to us, at which point we applied the band-aid solution. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Alex Williamson
2007-May-09 15:38 UTC
Re: [Xen-devel] Is patches/linux-2.6.18/xen-hotplug.patch still necessary?
On Wed, 2007-05-09 at 16:32 +0100, Keir Fraser wrote:> On 9/5/07 16:07, "Alex Williamson" <alex.williamson@hp.com> wrote: > > >> It has to be handled in top itself. With some versions at least it was the > >> case that top would crash when CPUs where hot-unplugged. If you revert that > >> patch, does your version of top work okay in the hot-unplug case (you have > >> to run top across the unplug operation to see if it will crash or not)? > > > > Top still crashes without that patch, but the patch just hides the > > problem. Top also crashes during a CPU hotplug operation on bare metal. > > I think this patch causes more problems than if fixes. Thanks, > > The fact that physical CPU hotplug is an incredibly rare operation, even on > the 0.001% of all systems that it is actually supported on, compared with > virtual CPU hotplug being potentially quite frequent, is a real concern. > Users are actually moderately likely to see this bug when running on Xen. In > fact they used to, and then they complained to us, at which point we applied > the band-aid solution.Likewise, I''ve had users complain that the sysconf(_SC_NPROCESSORS_ONLN) fails to report the correct number of online CPUs with this patch. Thanks, Alex -- Alex Williamson HP Open Source & Linux Org. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel