Messages in this thread Patch in this message | | | From | Andy Shevchenko <> | Subject | [PATCH v1 1/1] cpumask: Don't waste memory for sysfs cpulist nodes | Date | Thu, 22 Sep 2022 22:34:47 +0300 |
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Currently the approximation is used which wastes the more memory the more CPUs are present on the system. Proposed change calculates the exact maximum needed in the worst case:
NR_CPUS old new ------- --- --- 1 .. 1860 4096 4096 ... ... ... 2*4096 28672 19925 4*4096 57344 43597 8*4096 114688 92749 16*4096 229376 191053 32*4096 458752 403197 64*4096 917504 861949 128*4096 1835008 1779453 256*4096 3670016 3670016
Under the hood the reccurent formula is being used: (5 - 0) * 2 + (50 - 5) * 3 + (500 - 50) * 4 + (5000 - 500) * 5 + ... (X[i] - X[i-1]) * i
which allows to count the exact maximum length in the worst case, i.e. when each second CPU is being listed. For less than 1861 and more than 1 million CPUs the old is being used.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> --- include/linux/cpumask.h | 45 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index 1b442fb2001f..7c6416fa038d 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -1122,6 +1122,18 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, * * for cpumap NR_CPUS * 9/32 - 1 should be an exact length. * + * for cpulist the reccurent formula is being used: + * (5 - 0) * 2 + + * (50 - 5) * 3 + + * (500 - 50) * 4 + + * (5000 - 500) * 5 + + * ... + * (X[i] - X[i-1]) * i + * + * which allows to count the exact maximum length in the worst case, + * i.e. when each second CPU is being listed. For less than 1861 and + * more than 1 million CPUs the old is being used as described below: + * * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up * to 2 orders of magnitude larger than 8192. And then we divide by 2 to * cover a worst-case of every other cpu being on one of two nodes for a @@ -1132,6 +1144,39 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, */ #define CPUMAP_FILE_MAX_BYTES (((NR_CPUS * 9)/32 > PAGE_SIZE) \ ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE) + +#define __CPULIST_FOR_10(x) (((x + 1) / 2 - 0) * 2) +#define __CPULIST_FOR_100(x) (((x + 1) / 2 - 5) * 3) +#define __CPULIST_FOR_1000(x) (((x + 1) / 2 - 50) * 4) +#define __CPULIST_FOR_10000(x) (((x + 1) / 2 - 500) * 5) +#define __CPULIST_FOR_100000(x) (((x + 1) / 2 - 5000) * 6) +#define __CPULIST_FOR_1000000(x) (((x + 1) / 2 - 50000) * 7) + +#if NR_CPUS < 1861 +#define CPULIST_FILE_MAX_BYTES PAGE_SIZE +#elif NR_CPUS < 10000 +#define CPULIST_FILE_MAX_BYTES \ + (__CPULIST_FOR_10(10) + \ + __CPULIST_FOR_100(100) + \ + __CPULIST_FOR_1000(1000) + \ + __CPULIST_FOR_10000(NR_CPUS)) +#elif NR_CPUS < 100000 +#define CPULIST_FILE_MAX_BYTES \ + (__CPULIST_FOR_10(10) + \ + __CPULIST_FOR_100(100) + \ + __CPULIST_FOR_1000(1000) + \ + __CPULIST_FOR_10000(10000) + \ + __CPULIST_FOR_100000(NR_CPUS)) +#elif NR_CPUS < 1000000 +#define CPULIST_FILE_MAX_BYTES \ + (__CPULIST_FOR_10(10) + \ + __CPULIST_FOR_100(100) + \ + __CPULIST_FOR_1000(1000) + \ + __CPULIST_FOR_10000(10000) + \ + __CPULIST_FOR_100000(100000) + \ + __CPULIST_FOR_1000000(NR_CPUS)) +#else #define CPULIST_FILE_MAX_BYTES (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE) +#endif #endif /* __LINUX_CPUMASK_H */ -- 2.35.1
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