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>
> ---
> 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