On 7/19/23 14:34, kernel test robot wrote:
I noticed that the struct mm_struct has following layout change after this patch.
hi, Mathieu Desnoyers,
we noticed that this commit addressed issue:
"[linus:master] [sched] af7f588d8f: will-it-scale.per_thread_ops -13.9% regression"
we reported before on:
https://lore.kernel.org/oe-lkp/202305151017.27581d75-yujie.liu@xxxxxxxxx/
we really saw a will-it-scale.per_thread_ops 92.2% improvement by this commit
(details are as below).
however, we also noticed a stress-ng regression.
below detail report FYI.
Hello,
kernel test robot noticed a -6.5% regression of stress-ng.madvise.ops_per_sec on:
commit: c1753fd02a0058ea43cbb31ab26d25be2f6cfe08 ("mm: move mm_count into its own cache line")
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
Without the patch:
spinlock_t page_table_lock; /* 124 4 */
/* --- cacheline 2 boundary (128 bytes) --- */
struct rw_semaphore mmap_lock; /* 128 40 */ ----> in one cache line
struct list_head mmlist; /* 168 16 */
int mm_lock_seq; /* 184 4 */
With the patch:
spinlock_t page_table_lock; /* 180 4 */
struct rw_semaphore mmap_lock; /* 184 40 */ ----> cross to two cache lines
/* --- cacheline 3 boundary (192 bytes) was 32 bytes ago --- */
struct list_head mmlist; /* 224 16 */