On Wed, Nov 24, 2021 at 04:47:20PM -0800, Paul E. McKenney wrote: > On Tue, Nov 23, 2021 at 01:37:07AM +0100, Frederic Weisbecker wrote: > > If a user wants to boot without any CPU in offloaded mode initially but > > with the possibility to offload them later using cpusets, provide a way > > to simply pass an empty "rcu_nocbs" kernel parameter which will enforce > > the creation of dormant nocb kthreads. > > Huh. This would have been a use for Yury Norov's "none" bitmask > specifier. ;-) > > I pulled this one in with the usual wordsmithing. > > Thanx, Paul I think 'rcu_nocbs=,' should work as 'none'. But I admit that it looks awkward. The following patch adds clear 'none' semantics to the parser. If you like it, I think you may drop non-documentation part of this patch. >From e3a9cfe4830141c88aa5d8a93eae3512b2ae2882 Mon Sep 17 00:00:00 2001 From: Yury Norov <yury.norov@xxxxxxxxx> Date: Wed, 24 Nov 2021 19:34:05 -0800 Subject: [PATCH] lib/bitmap: add 'none' specifier for bitmap_parselist() Currently bitmap_parselist() has no clear notation to specify empty bitmap. The format allows ',' or '0:0-N' for doing this, but it looks hacky. Frederic Weisbecker needs to pass an empty rcu_nocbs to the kernel, and without such a notation has to hack his own code: https://lore.kernel.org/rcu/20211125005526.GA490855@lothringen/ This patch adds 'none' to the bitmap_parselist, so that no such hacks would be needed. 'None' is case-insensitive and doesn't support group semantics ('none:1/2' is meaningless and wouldn't work). Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx> --- Documentation/admin-guide/kernel-parameters.rst | 7 +++++-- lib/bitmap.c | 12 +++++++++++- lib/test_bitmap.c | 13 +++++++++++++ 3 files changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst index 01ba293a2d70..af261018bab5 100644 --- a/Documentation/admin-guide/kernel-parameters.rst +++ b/Documentation/admin-guide/kernel-parameters.rst @@ -76,11 +76,14 @@ to change, such as less cores in the CPU list, then N and any ranges using N will also change. Use the same on a small 4 core system, and "16-N" becomes "16-3" and now the same boot input will be flagged as invalid (start > end). +The special case-tolerant group name "none" has a meaning of selecting no CPUs, +so that "rcu_nocps=none" would allow to disable offloading mode for all CPUs. + The special case-tolerant group name "all" has a meaning of selecting all CPUs, so that "nohz_full=all" is the equivalent of "nohz_full=0-N". -The semantics of "N" and "all" is supported on a level of bitmaps and holds for -all users of bitmap_parse(). +The semantics of "none", "N" and "all" is supported on a level of bitmaps and +holds for all users of bitmap_parse(). This document may not be entirely up to date and comprehensive. The command "modinfo -p ${modulename}" shows a current list of all parameters of a loadable diff --git a/lib/bitmap.c b/lib/bitmap.c index d7b80a069819..bcb38d055ec1 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -771,6 +771,16 @@ static const char *bitmap_parse_region(const char *str, struct region *r) goto check_pattern; } + if (!strncasecmp(str, "none", 4)) { + r->start = 0; + r->end = 0; + r->off = 0; + r->group_len = r->nbits; + str += 4; + + goto out; + } + str = bitmap_getnum(str, &r->start, lastbit); if (IS_ERR(str)) return str; @@ -806,7 +816,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r) no_pattern: r->off = r->end + 1; r->group_len = r->end + 1; - +out: return end_of_str(*str) ? NULL : str; } diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c index 0c82f07f74fc..1111d0d0df5f 100644 --- a/lib/test_bitmap.c +++ b/lib/test_bitmap.c @@ -351,18 +351,26 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = { {0, ",, ,, , , ,", &exp1[12 * step], 8, 0}, {0, " , ,, , , ", &exp1[12 * step], 8, 0}, {0, " , ,, , , \n", &exp1[12 * step], 8, 0}, + {0, "none", &exp1[12 * step], 8, 0}, + {0, " , NONE ,, , , \n", &exp1[12 * step], 8, 0}, + {0, " , ,none, , , \n", &exp1[12 * step], 8, 0}, + {0, " , ,, , ,none \n", &exp1[12 * step], 8, 0}, {0, "0-0", &exp1[0], 32, 0}, {0, "1-1", &exp1[1 * step], 32, 0}, {0, "15-15", &exp1[13 * step], 32, 0}, {0, "31-31", &exp1[14 * step], 32, 0}, + {0, "31-31,none", &exp1[14 * step], 32, 0}, {0, "0-0:0/1", &exp1[12 * step], 32, 0}, + {0, "0-0:0/1,none", &exp1[12 * step], 32, 0}, {0, "0-0:1/1", &exp1[0], 32, 0}, {0, "0-0:1/31", &exp1[0], 32, 0}, {0, "0-0:31/31", &exp1[0], 32, 0}, {0, "1-1:1/1", &exp1[1 * step], 32, 0}, {0, "0-15:16/31", &exp1[2 * step], 32, 0}, + {0, "0-15:16/31,none", &exp1[2 * step], 32, 0}, + {0, "none,0-15:16/31", &exp1[2 * step], 32, 0}, {0, "15-15:1/2", &exp1[13 * step], 32, 0}, {0, "15-15:31/31", &exp1[13 * step], 32, 0}, {0, "15-31:1/31", &exp1[13 * step], 32, 0}, @@ -381,6 +389,7 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = { {0, "0-N:1/3,1-N:1/3,2-N:1/3", &exp1[8 * step], 32, 0}, {0, "0-31:1/3,1-31:1/3,2-31:1/3", &exp1[8 * step], 32, 0}, {0, "1-10:8/12,8-31:24/29,0-31:0/3", &exp1[9 * step], 32, 0}, + {0, "1-10:8/12,none,8-31:24/29,0-31:0/3", &exp1[9 * step], 32, 0}, {0, "all", &exp1[8 * step], 32, 0}, {0, "0, 1, all, ", &exp1[8 * step], 32, 0}, @@ -388,6 +397,10 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = { {0, "ALL:1/2", &exp1[4 * step], 32, 0}, {-EINVAL, "al", NULL, 8, 0}, {-EINVAL, "alll", NULL, 8, 0}, + {-EINVAL, "non", NULL, 8, 0}, + {-EINVAL, "one", NULL, 8, 0}, + {-EINVAL, "NONEE", NULL, 8, 0}, + {-EINVAL, "NONE:1/2", NULL, 8, 0}, {-EINVAL, "-1", NULL, 8, 0}, {-EINVAL, "-0", NULL, 8, 0}, -- 2.25.1
