diff options
author | Paul Gortmaker <paul.gortmaker@windriver.com> | 2021-02-21 11:08:25 +0300 |
---|---|---|
committer | Paul E. McKenney <paulmck@kernel.org> | 2021-03-09 01:16:58 +0300 |
commit | 2c4885d24e64941702a8f81c8e83289823ba35d0 (patch) | |
tree | e873dad739f3b0f531c38d580ef46423ec79edf1 /lib | |
parent | f3c869caef648c541a7445f2a6ba2196d343f542 (diff) | |
download | linux-2c4885d24e64941702a8f81c8e83289823ba35d0.tar.xz |
lib: bitmap: support "N" as an alias for size of bitmap
While this is done for all bitmaps, the original use case in mind was
for CPU masks and cpulist_parse() as described below.
It seems that a common configuration is to use the 1st couple cores for
housekeeping tasks. This tends to leave the remaining ones to form a
pool of similarly configured cores to take on the real workload of
interest to the user.
So on machine A - with 32 cores, it could be 0-3 for "system" and then
4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
setting up the worker pool of CPUs.
But then newer machine B is added, and it has 48 cores, and so while
the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.
Multiple deployment becomes easier when we can just simply replace 31
and 47 with "N" and let the system substitute in the actual number at
boot; a number that it knows better than we do.
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Yury Norov <yury.norov@gmail.com> # move it from CPU code
Acked-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/bitmap.c | 22 |
1 files changed, 17 insertions, 5 deletions
diff --git a/lib/bitmap.c b/lib/bitmap.c index 833f152a2c43..9f4626a4c95f 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -519,11 +519,17 @@ static int bitmap_check_region(const struct region *r) return 0; } -static const char *bitmap_getnum(const char *str, unsigned int *num) +static const char *bitmap_getnum(const char *str, unsigned int *num, + unsigned int lastbit) { unsigned long long n; unsigned int len; + if (str[0] == 'N') { + *num = lastbit; + return str + 1; + } + len = _parse_integer(str, 10, &n); if (!len) return ERR_PTR(-EINVAL); @@ -571,7 +577,9 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end static const char *bitmap_parse_region(const char *str, struct region *r) { - str = bitmap_getnum(str, &r->start); + unsigned int lastbit = r->nbits - 1; + + str = bitmap_getnum(str, &r->start, lastbit); if (IS_ERR(str)) return str; @@ -581,7 +589,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r) if (*str != '-') return ERR_PTR(-EINVAL); - str = bitmap_getnum(str + 1, &r->end); + str = bitmap_getnum(str + 1, &r->end, lastbit); if (IS_ERR(str)) return str; @@ -591,14 +599,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r) if (*str != ':') return ERR_PTR(-EINVAL); - str = bitmap_getnum(str + 1, &r->off); + str = bitmap_getnum(str + 1, &r->off, lastbit); if (IS_ERR(str)) return str; if (*str != '/') return ERR_PTR(-EINVAL); - return bitmap_getnum(str + 1, &r->group_len); + return bitmap_getnum(str + 1, &r->group_len, lastbit); no_end: r->end = r->start; @@ -625,6 +633,10 @@ no_pattern: * From each group will be used only defined amount of bits. * Syntax: range:used_size/group_size * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769 + * The value 'N' can be used as a dynamically substituted token for the + * maximum allowed value; i.e (nmaskbits - 1). Keep in mind that it is + * dynamic, so if system changes cause the bitmap width to change, such + * as more cores in a CPU list, then any ranges using N will also change. * * Returns: 0 on success, -errno on invalid input strings. Error values: * |