Re: [libvirt] [PATCH 1/1] nodeinfo: Increase the num of CPU thread siblings to a larger value

On 03/26/2015 07:03 AM, Ján Tomko wrote: > On Thu, Mar 26, 2015 at 12:48:13AM -0400, Wei Huang wrote: >> Current libvirt can only handle up to 1024 thread siblings when it >> reads Linux sysfs topology/thread_siblings. This isn't enough for >> Linux distributions that support a large value. This patch fixes >> the problem by using VIR_ALLOC()/VIR_FREE(), instead of using a >> fixed-size (1024) local char array. In the meanwhile >> SYSFS_THREAD_SIBLINGS_LIST_LENGTH_MAX is increased to 8192 which >> should be large enough for a foreseeable future. >> >> Signed-off-by: Wei Huang <wei(a)redhat.com&gt; >> --- >> src/nodeinfo.c | 10 +++++++--- >> 1 file changed, 7 insertions(+), 3 deletions(-) >> >> diff --git a/src/nodeinfo.c b/src/nodeinfo.c >> index 34d27a6..66dc7ef 100644 >> --- a/src/nodeinfo.c >> +++ b/src/nodeinfo.c >> @@ -287,7 +287,7 @@ freebsdNodeGetMemoryStats(virNodeMemoryStatsPtr >> params, >> # define PROCSTAT_PATH "/proc/stat" >> # define MEMINFO_PATH "/proc/meminfo" >> # define SYSFS_MEMORY_SHARED_PATH "/sys/kernel/mm/ksm" >> -# define SYSFS_THREAD_SIBLINGS_LIST_LENGTH_MAX 1024 >> +# define SYSFS_THREAD_SIBLINGS_LIST_LENGTH_MAX 8192 > > There is thread_siblings_list, which contains a range: > 22-23 > and thread_siblings file has all the bits set: > 00c00000 > > For the second one, the 1024-byte buffer should be enough for 16368 > possible siblings. > a 4096 siblings file will generate a (cpumask_t -based) output of : 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000080 9(characters per 32-bit mask, including the comma)*8(masks/row)*16(rows) -1(last entry doesn't have a comma) = 1152 Other releases/arch's avoid this issue by using cpumask_var_t vs cpumask_t for siblings so it's reflective of actual cpu count a system (not operating system) could provide/support.

cpumask_t objects are NR_CPUS -sized. In the not so distant future, though, real systems will have 1024 cpus, so might as well accomodate for a couple years after that.

> For the first one, the results depend on the topology - if the sibling > ranges are contiguous, even million CPUs should fit there. The _list files(core_siblings_list, thread_siblings_list) have ranges; the non _list (core_siblings, thread_siblings) files have mask like above. > For the worst case, when every other cpu is a sibling, the second file > is more space-efficient. > > > I'm OK with using the same limit for both (8k seems sufficiently large), > but I would like to know: > > Which one is the file that failed to parse in your case? > /sys/devices/system/cpu/cpu*/topology/thread_siblings > I think both virNodeCountThreadSiblings and virNodeGetSiblingsList could > be rewritten to share some code and only look at one of the sysfs files. > The question is - which one? > > Jan >