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From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: linux-kernel@vger.kernel.org
Cc: lizefan@huawei.com, mingo@kernel.org, tglx@linutronix.de,
	josh@joshtriplett.org, yury.norov@gmail.com,
	peterz@infradead.org, paulmck@kernel.org, fweisbec@gmail.com,
	linux@rasmusvillemoes.dk, andriy.shevchenko@linux.intel.com,
	Paul Gortmaker <paul.gortmaker@windriver.com>
Subject: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap
Date: Tue, 26 Jan 2021 12:11:39 -0500	[thread overview]
Message-ID: <20210126171141.122639-7-paul.gortmaker@windriver.com> (raw)
In-Reply-To: <20210126171141.122639-1-paul.gortmaker@windriver.com>

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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 Documentation/admin-guide/kernel-parameters.rst |  2 ++
 lib/bitmap.c                                    | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 682ab28b5c94..850917f19476 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -68,6 +68,8 @@ For example one can add to the command line following parameter:
 
 where the final item represents CPUs 100,101,125,126,150,151,...
 
+The value "N" can be used to represent the numerically last CPU on the system,
+i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
 
 
 This document may not be entirely up to date and comprehensive. The command
diff --git a/lib/bitmap.c b/lib/bitmap.c
index f65be2f148fd..2fdd00b312c3 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 nbits,
+				    unsigned int *num)
 {
 	unsigned long long n;
 	unsigned int len;
 
+	if (str[0] == 'N') {
+		*num = nbits - 1;
+		return str + 1;
+	}
+
 	len = _parse_integer(str, 10, &n);
 	if (!len)
 		return ERR_PTR(-EINVAL);
@@ -533,7 +539,7 @@ static const char *bitmap_getnum(const char *str, unsigned int *num)
 	*num = n;
 	return str + len;
 }
-#define bitmap_getrnum(s, r, pos) bitmap_getnum(s, &(r->pos))
+#define bitmap_getrnum(s, r, pos) __bitmap_getnum(s, r->nbits, &(r->pos))
 
 static inline bool end_of_str(char c)
 {
@@ -626,6 +632,8 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
  * 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).
  *
  * Returns: 0 on success, -errno on invalid input strings. Error values:
  *
-- 
2.17.1


  parent reply	other threads:[~2021-01-27  0:28 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 17:11 [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Paul Gortmaker
2021-01-26 17:11 ` [PATCH 1/8] lib: test_bitmap: clearly separate ERANGE from EINVAL tests Paul Gortmaker
2021-01-26 21:04   ` Andy Shevchenko
2021-01-27  7:21     ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 2/8] lib: test_bitmap: add more start-end:offset/len tests Paul Gortmaker
2021-01-26 21:11   ` Andy Shevchenko
2021-01-27  3:03   ` Yury Norov
2021-01-26 17:11 ` [PATCH 3/8] lib: bitmap: fold nbits into region struct Paul Gortmaker
2021-01-26 21:16   ` Andy Shevchenko
2021-01-26 21:18     ` Andy Shevchenko
2021-01-27  8:02     ` Paul Gortmaker
2021-01-28  0:47       ` Yury Norov
2021-01-28 10:17         ` Andy Shevchenko
2021-01-27  3:08   ` Yury Norov
2021-01-26 17:11 ` [PATCH 4/8] lib: bitmap: move ERANGE check from set_region to check_region Paul Gortmaker
2021-01-26 21:19   ` Andy Shevchenko
2021-01-27  3:12   ` Yury Norov
2021-01-26 17:11 ` [PATCH 5/8] lib: bitmap_getnum: separate arg into region and field Paul Gortmaker
2021-01-26 21:23   ` Andy Shevchenko
2021-01-27  2:58     ` Yury Norov
2021-01-27  8:38       ` Paul Gortmaker
2021-01-26 17:11 ` Paul Gortmaker [this message]
2021-01-26 21:37   ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Andy Shevchenko
2021-01-26 21:41     ` Andy Shevchenko
2021-01-27 17:57       ` Yury Norov
2021-01-27  8:20     ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 7/8] lib: test_bitmap: add tests for "N" alias Paul Gortmaker
2021-01-26 17:11 ` [PATCH 8/8] rcu: deprecate "all" option to rcu_nocbs= Paul Gortmaker
2021-01-26 21:36   ` Yury Norov
2021-01-26 22:17     ` Paul E. McKenney
2021-01-26 22:27 ` [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Yury Norov
2021-01-27  9:12   ` Paul Gortmaker
2021-02-09 22:58 [PATCH v4 " Paul Gortmaker
2021-02-09 22:59 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-02-09 23:16   ` Yury Norov
2021-02-10 15:58     ` Paul Gortmaker
2021-02-10 16:49       ` Andy Shevchenko
2021-02-12  1:24         ` Yury Norov
2021-02-21  8:07           ` Paul Gortmaker
2021-02-21  8:08 [PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation Paul Gortmaker
2021-02-21  8:08 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker

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