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Date: Wed, 24 Nov 2021 20:41:32 -0800
From: Yury Norov <yury.norov@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Uladzislau Rezki <urezki@...il.com>,
Neeraj Upadhyay <quic_neeraju@...cinc.com>,
Boqun Feng <boqun.feng@...il.com>,
Josh Triplett <josh@...htriplett.org>,
Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-doc@...r.kernel.org
Subject: Re: [PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter
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@...il.com>
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@...il.com>
---
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
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