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>
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@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
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where the final item represents CPUs 100,101,125,126,150,151,...
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where the final item represents CPUs 100,101,125,126,150,151,...
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The value "N" can be used to represent the numerically last CPU on the system,
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i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
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Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
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to change, such as less cores in the CPU list, then N and any ranges using N
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will also change. Use the same on a small 4 core system, and "16-N" becomes
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"16-3" and now the same boot input will be flagged as invalid (start > end).
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This document may not be entirely up to date and comprehensive. The command
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This document may not be entirely up to date and comprehensive. The command
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22
lib/bitmap.c
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lib/bitmap.c
@ -519,11 +519,17 @@ static int bitmap_check_region(const struct region *r)
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return 0;
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return 0;
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}
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}
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static const char *bitmap_getnum(const char *str, unsigned int *num)
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static const char *bitmap_getnum(const char *str, unsigned int *num,
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unsigned int lastbit)
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{
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{
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unsigned long long n;
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unsigned long long n;
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unsigned int len;
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unsigned int len;
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if (str[0] == 'N') {
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*num = lastbit;
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return str + 1;
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}
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len = _parse_integer(str, 10, &n);
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len = _parse_integer(str, 10, &n);
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if (!len)
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if (!len)
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return ERR_PTR(-EINVAL);
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return ERR_PTR(-EINVAL);
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@ -571,7 +577,9 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end
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static const char *bitmap_parse_region(const char *str, struct region *r)
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static const char *bitmap_parse_region(const char *str, struct region *r)
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{
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{
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str = bitmap_getnum(str, &r->start);
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unsigned int lastbit = r->nbits - 1;
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str = bitmap_getnum(str, &r->start, lastbit);
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if (IS_ERR(str))
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if (IS_ERR(str))
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return str;
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return str;
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@ -581,7 +589,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
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if (*str != '-')
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if (*str != '-')
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return ERR_PTR(-EINVAL);
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return ERR_PTR(-EINVAL);
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str = bitmap_getnum(str + 1, &r->end);
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str = bitmap_getnum(str + 1, &r->end, lastbit);
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if (IS_ERR(str))
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if (IS_ERR(str))
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return str;
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return str;
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@ -591,14 +599,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
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if (*str != ':')
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if (*str != ':')
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return ERR_PTR(-EINVAL);
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return ERR_PTR(-EINVAL);
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str = bitmap_getnum(str + 1, &r->off);
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str = bitmap_getnum(str + 1, &r->off, lastbit);
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if (IS_ERR(str))
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if (IS_ERR(str))
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return str;
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return str;
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if (*str != '/')
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if (*str != '/')
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return ERR_PTR(-EINVAL);
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return ERR_PTR(-EINVAL);
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return bitmap_getnum(str + 1, &r->group_len);
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return bitmap_getnum(str + 1, &r->group_len, lastbit);
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no_end:
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no_end:
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r->end = r->start;
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r->end = r->start;
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@ -625,6 +633,10 @@ no_pattern:
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* From each group will be used only defined amount of bits.
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* From each group will be used only defined amount of bits.
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* Syntax: range:used_size/group_size
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* Syntax: range:used_size/group_size
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* Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
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* Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
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* The value 'N' can be used as a dynamically substituted token for the
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* maximum allowed value; i.e (nmaskbits - 1). Keep in mind that it is
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* dynamic, so if system changes cause the bitmap width to change, such
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* as more cores in a CPU list, then any ranges using N will also change.
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*
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*
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* Returns: 0 on success, -errno on invalid input strings. Error values:
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* Returns: 0 on success, -errno on invalid input strings. Error values:
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*
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*
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