From 126310c9f669c9a8c875a3e5c2292299ca90225d Mon Sep 17 00:00:00 2001 From: K Prateek Nayak Date: Mon, 8 May 2023 14:11:14 +0530 Subject: [PATCH 1/2] drivers: base: cacheinfo: Fix shared_cpu_map changes in event of CPU hotplug While building the shared_cpu_map, check if the cache level and cache type matches. On certain systems that build the cache topology based on the instance ID, there are cases where the same ID may repeat across multiple cache levels, leading inaccurate topology. In event of CPU offlining, the cache_shared_cpu_map_remove() does not consider if IDs at same level are being compared. As a result, when same IDs repeat across different cache levels, the CPU going offline is not removed from all the shared_cpu_map. Below is the output of cache topology of CPU8 and it's SMT sibling after CPU8 is offlined on a dual socket 3rd Generation AMD EPYC processor (2 x 64C/128T) running kernel release v6.3: # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143 # echo 0 > /sys/devices/system/cpu/cpu8/online # for i in /sys/devices/system/cpu/cpu136/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list: 136 /sys/devices/system/cpu/cpu136/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu136/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list: 9-15,136-143 CPU8 is removed from index0 (L1i) but remains in the shared_cpu_list of index1 (L1d) and index2 (L2). Since L1i, L1d, and L2 are shared by the SMT siblings, and they have the same cache instance ID, CPU 2 is only removed from the first index with matching ID which is index1 (L1i) in this case. With this fix, the results are as expected when performing the same experiment on the same system: # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143 # echo 0 > /sys/devices/system/cpu/cpu8/online # for i in /sys/devices/system/cpu/cpu136/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list: 136 /sys/devices/system/cpu/cpu136/cache/index1/shared_cpu_list: 136 /sys/devices/system/cpu/cpu136/cache/index2/shared_cpu_list: 136 /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list: 9-15,136-143 When rebuilding topology, the same problem appears as cache_shared_cpu_map_setup() implements a similar logic. Consider the same 3rd Generation EPYC processor: CPUs in Core 1, that share the L1 and L2 caches, have L1 and L2 instance ID as 1. For all the CPUs on the second chiplet, the L3 ID is also 1 leading to grouping on CPUs from Core 1 (1, 17) and the entire second chiplet (8-15, 24-31) as CPUs sharing one cache domain. This went undetected since x86 processors depended on arch specific populate_cache_leaves() method to repopulate the shared_cpus_map when CPU came back online until kernel release v6.3-rc5. Fixes: 198102c9103f ("cacheinfo: Fix shared_cpu_map to handle shared caches at different levels") Signed-off-by: K Prateek Nayak Reviewed-by: Sudeep Holla Link: https://lore.kernel.org/r/20230508084115.1157-2-kprateek.nayak@amd.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/cacheinfo.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c index bba3482ddeb82..d1ae443fd7a07 100644 --- a/drivers/base/cacheinfo.c +++ b/drivers/base/cacheinfo.c @@ -388,6 +388,16 @@ static int cache_shared_cpu_map_setup(unsigned int cpu) continue;/* skip if itself or no cacheinfo */ for (sib_index = 0; sib_index < cache_leaves(i); sib_index++) { sib_leaf = per_cpu_cacheinfo_idx(i, sib_index); + + /* + * Comparing cache IDs only makes sense if the leaves + * belong to the same cache level of same type. Skip + * the check if level and type do not match. + */ + if (sib_leaf->level != this_leaf->level || + sib_leaf->type != this_leaf->type) + continue; + if (cache_leaves_are_shared(this_leaf, sib_leaf)) { cpumask_set_cpu(cpu, &sib_leaf->shared_cpu_map); cpumask_set_cpu(i, &this_leaf->shared_cpu_map); @@ -419,6 +429,16 @@ static void cache_shared_cpu_map_remove(unsigned int cpu) for (sib_index = 0; sib_index < cache_leaves(sibling); sib_index++) { sib_leaf = per_cpu_cacheinfo_idx(sibling, sib_index); + + /* + * Comparing cache IDs only makes sense if the leaves + * belong to the same cache level of same type. Skip + * the check if level and type do not match. + */ + if (sib_leaf->level != this_leaf->level || + sib_leaf->type != this_leaf->type) + continue; + if (cache_leaves_are_shared(this_leaf, sib_leaf)) { cpumask_clear_cpu(cpu, &sib_leaf->shared_cpu_map); cpumask_clear_cpu(sibling, &this_leaf->shared_cpu_map); From c26fabe73330d983c7ce822c6b6ec0879b4da61f Mon Sep 17 00:00:00 2001 From: K Prateek Nayak Date: Mon, 8 May 2023 14:11:15 +0530 Subject: [PATCH 2/2] drivers: base: cacheinfo: Update cpu_map_populated during CPU Hotplug Until commit 5c2712387d48 ("cacheinfo: Fix LLC is not exported through sysfs"), cacheinfo called populate_cache_leaves() for CPU coming online which let the arch specific functions handle (at least on x86) populating the shared_cpu_map. However, with the changes in the aforementioned commit, populate_cache_leaves() is not called when a CPU comes online as a result of hotplug since last_level_cache_is_valid() returns true as the cacheinfo data is not discarded. The CPU coming online is not present in shared_cpu_map, however, it will not be added since the cpu_cacheinfo->cpu_map_populated flag is set (it is set in populate_cache_leaves() when cacheinfo is first populated for x86) This can lead to inconsistencies in the shared_cpu_map when an offlined CPU comes online again. Example below depicts the inconsistency in the shared_cpu_list in cacheinfo when CPU8 is offlined and onlined again on a 3rd Generation EPYC processor: # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143 # echo 0 > /sys/devices/system/cpu/cpu8/online # echo 1 > /sys/devices/system/cpu/cpu8/online # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8 # cat /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list 136 # cat /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list 9-15,136-143 Clear the flag when the CPU is removed from shared_cpu_map when cache_shared_cpu_map_remove() is called during CPU hotplug. This will allow cache_shared_cpu_map_setup() to add the CPU coming back online in the shared_cpu_map. Set the flag again when the shared_cpu_map is setup. Following are results of performing the same test as described above with the changes: # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143 # echo 0 > /sys/devices/system/cpu/cpu8/online # echo 1 > /sys/devices/system/cpu/cpu8/online # for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done /sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136 /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143 # cat /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list 8,136 # cat /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list 8-15,136-143 Fixes: 5c2712387d48 ("cacheinfo: Fix LLC is not exported through sysfs") Signed-off-by: K Prateek Nayak Reviewed-by: Yicong Yang Reviewed-by: Sudeep Holla Link: https://lore.kernel.org/r/20230508084115.1157-3-kprateek.nayak@amd.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/cacheinfo.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c index d1ae443fd7a07..cbae8be1fe520 100644 --- a/drivers/base/cacheinfo.c +++ b/drivers/base/cacheinfo.c @@ -410,11 +410,14 @@ static int cache_shared_cpu_map_setup(unsigned int cpu) coherency_max_size = this_leaf->coherency_line_size; } + /* shared_cpu_map is now populated for the cpu */ + this_cpu_ci->cpu_map_populated = true; return 0; } static void cache_shared_cpu_map_remove(unsigned int cpu) { + struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu); struct cacheinfo *this_leaf, *sib_leaf; unsigned int sibling, index, sib_index; @@ -447,6 +450,9 @@ static void cache_shared_cpu_map_remove(unsigned int cpu) } } } + + /* cpu is no longer populated in the shared map */ + this_cpu_ci->cpu_map_populated = false; } static void free_cache_attributes(unsigned int cpu)