Re: [Xen-devel] xl vcpu-pin peculiarities in core scheduling mode
On Tue, 2020-03-24 at 15:22 +0100, Jürgen Groß wrote: > On 24.03.20 14:34, Sergey Dyasli wrote: > > I did some experiments and noticed > > the following > > inconsistencies: > > > >1. xl vcpu-pin 5 0 0 > > Windows 10 (64-bit) (1) 5 00 > > -b-1644.0 0 / all > > Windows 10 (64-bit) (1) 5 11 > > -b-1650.1 0 / all > > ^ > > ^ > > CPU 1 doesn't match reported hard-affinity of 0. Should this > > command set > > hard-affinity of vCPU 1 to 1? Or should it be 0-1 for both > > vCPUs instead? > > I think this is fine. For improving how this is reported back to users, I'd go for the solution nr 3 proposed by Juergen (below). > >2. xl vcpu-pin 5 0 1 > > libxl: error: libxl_sched.c:62:libxl__set_vcpuaffinity: > > Domain 5:Setting vcpu affinity: Invalid argument > > This is expected but perhaps needs documenting somewhere? > > Not against more clear error reporting. It would mean that libxl must have a way to tell that pinning failed because pinning was not being done to a "master CPU". I guess it's doable, but perhaps it's not the top priority, assuming we have (and we put in place, if we still don't) good documentation on how pinning works in this operational mode. That would make a good article/blog post, I think. > >3. xl vcpu-pin 5 0 1-2 > > Windows 10 (64-bit) (1) 5 02 > > -b-1646.7 1-2 / all > > Windows 10 (64-bit) (1) 5 13 > > -b-1651.6 1-2 / all > > ^ > > ^^^ > > Here is a CPU / affinity mismatch again, but the more > > interesting fact > > is that setting 1-2 is allowed at all, I'd expect CPU would > > never be set > > to 1 with such settings. > > This is the situation I'm most concerned of. Mostly, because I think a user might be surprised to see the command (1) not failing and (2) having the effect that it has. I think that, in this case, we should either fail, or adjust the affinity to 2-3. If we do the latter, we should inform the user about that. There's something similar in libxl already (related to soft and hard affinity, where we set a mask, then we check what's been actually setup by Xen and act accordingly). Thoughts? I'd go for a mix of 1 and 3, i.e., I'd do: > 1. As today, documenting the output. > Not very nice IMO, but the least effort. > This, i.e., we definitely need more documentation and we need to make sure it's visible enough. > 2. Just print one line for each virtual cpu/core/socket, like: > Windows 10 (64-bit) (1)5 0-1 0-1 -b-1646.7 0-1 / > all > This has the disadvantage of dropping the per-vcpu time in favor > of > per-vcore time, OTOH this is reflecting reality. > > 3. Print the effective pinnings: > Windows 10 (64-bit) (1)5 0 0 -b-1646.7 0 / > all > Windows 10 (64-bit) (1)5 1 1 -b-1646.7 1 / > all > Should be rather easy to do. > And this: i.e., I'd always report the effective mapping. I actually would go as far as changing the mapping we've been given and store the effective one(s) in `cpu_hard_affinity`, etc, in Xen. Of course, as said above, we'd need to inform the user that this has happened. Regards -- Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ --- <> (Raistlin Majere) signature.asc Description: This is a digitally signed message part
Re: [Xen-devel] xl vcpu-pin peculiarities in core scheduling mode
On 24.03.20 14:34, Sergey Dyasli wrote: Hi Juergen, I've notived there is no documentation about how vcpu-pin is supposed to work with core scheduling enabled. I did some experiments and noticed the following inconsistencies: 1. xl vcpu-pin 5 0 0 Windows 10 (64-bit) (1) 5 00 -b-1644.0 0 / all Windows 10 (64-bit) (1) 5 11 -b-1650.1 0 / all ^ ^ CPU 1 doesn't match reported hard-affinity of 0. Should this command set hard-affinity of vCPU 1 to 1? Or should it be 0-1 for both vCPUs instead? 2. xl vcpu-pin 5 0 1 libxl: error: libxl_sched.c:62:libxl__set_vcpuaffinity: Domain 5:Setting vcpu affinity: Invalid argument This is expected but perhaps needs documenting somewhere? 3. xl vcpu-pin 5 0 1-2 Windows 10 (64-bit) (1) 5 02 -b-1646.7 1-2 / all Windows 10 (64-bit) (1) 5 13 -b-1651.6 1-2 / all ^ ^^^ Here is a CPU / affinity mismatch again, but the more interesting fact is that setting 1-2 is allowed at all, I'd expect CPU would never be set to 1 with such settings. Please let me know what you think about the above cases. I think all of the effects can be explained by the way how pinning with core scheduling is implemented. This does not mean that the information presented to the user shouldn't be adapted. Basically pinning of any vcpu will just affect the "master"-vcpu of a virtual core (sibling 0). It will happily accept any setting as long as any "master"-cpu of a core is in the resulting set of cpus. All vcpus of a virtual core share the same pinnings. I think this explains all of the above scenarios. IMO there are the following possibilities for reporting those pinnings to the user: 1. As today, documenting the output. Not very nice IMO, but the least effort. 2. Just print one line for each virtual cpu/core/socket, like: Windows 10 (64-bit) (1)5 0-1 0-1 -b-1646.7 0-1 / all This has the disadvantage of dropping the per-vcpu time in favor of per-vcore time, OTOH this is reflecting reality. 3. Print the effective pinnings: Windows 10 (64-bit) (1)5 0 0 -b-1646.7 0 / all Windows 10 (64-bit) (1)5 1 1 -b-1646.7 1 / all Should be rather easy to do. Thoughts? Juergen
[Xen-devel] xl vcpu-pin peculiarities in core scheduling mode
Hi Juergen, I've notived there is no documentation about how vcpu-pin is supposed to work with core scheduling enabled. I did some experiments and noticed the following inconsistencies: 1. xl vcpu-pin 5 0 0 Windows 10 (64-bit) (1) 5 00 -b-1644.0 0 / all Windows 10 (64-bit) (1) 5 11 -b-1650.1 0 / all ^ ^ CPU 1 doesn't match reported hard-affinity of 0. Should this command set hard-affinity of vCPU 1 to 1? Or should it be 0-1 for both vCPUs instead? 2. xl vcpu-pin 5 0 1 libxl: error: libxl_sched.c:62:libxl__set_vcpuaffinity: Domain 5:Setting vcpu affinity: Invalid argument This is expected but perhaps needs documenting somewhere? 3. xl vcpu-pin 5 0 1-2 Windows 10 (64-bit) (1) 5 02 -b-1646.7 1-2 / all Windows 10 (64-bit) (1) 5 13 -b-1651.6 1-2 / all ^ ^^^ Here is a CPU / affinity mismatch again, but the more interesting fact is that setting 1-2 is allowed at all, I'd expect CPU would never be set to 1 with such settings. Please let me know what you think about the above cases. -- Thanks, Sergey