On 03/26/2015 12:08 PM, Wei Huang wrote:
On 03/26/2015 10:49 AM, Don Dutile wrote:
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@redhat.com> --- 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. Don, could ARM kernel use cpumask_var_t as well? Or this will require lots of change on top of existing code?
Yes. Working on that (kernel) patch now. It was simple/fast to use cpumask_t b/c historically, the counts (& kernel NR_CPUS value) were low. On x86, they were ACPI-driven. On arm64, need ACPI & DT-based solution, and arm64-acpi looks like it was based more on ia64 then x86, so need to create/support some new globals on arm64 that cpumask_var_t depend on, and have to roll DT to do the same.
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.
So we agree that such fix would be necessary, because: i) it will fail on cpumask_t based kernel (like Red Hat ARM); ii) eventually we might need to revisit this issue when a currently working system reaches the tipping point of CPU count (>1000).
Yes.
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