From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, 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
Subject: Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap
Date: Wed, 27 Jan 2021 03:20:47 -0500 [thread overview]
Message-ID: <20210127082046.GF23530@windriver.com> (raw)
In-Reply-To: <YBCLmrCSwBRkTAhT@smile.fi.intel.com>
[Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 26/01/2021 (Tue 23:37) Andy Shevchenko wrote:
> On Tue, Jan 26, 2021 at 12:11:39PM -0500, Paul Gortmaker wrote:
> > 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.
>
> I would accept lower 'n' as well.
>
> ...
>
> > -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;
> > + }
>
> But locating it here makes possible to enter a priori invalid input, like N for
> start of the region.
Actually, no. N can be valid input for start of the region - or for any
field in the region. I was originally thinking like you -- that N
was only valid as the end of the region, but Yury made a compelling
argument that N should be treated exactly as any other number is.
Skip down to where Yury says:
So, when I do echo N-N > cpuset.cpus, I want it to work as
if I do echo 15-15 > cpuset.cpus.
https://lore.kernel.org/lkml/20210126171811.GC23530@windriver.com/
You weren't Cc'd at that point as I'd not added any self-test changes
to the series yet - so you didn't probably see that discussion.
This is why you'll see "N-N:N/N" added as a self-test that works. It
doesn't make any more sense than using 15-15:15/15 does (vs. "15") but
both are equally valid inputs, in that they don't trigger an error.
Thanks,
Paul.
--
>
> I think this should be separate helper which is called in places where it makes
> sense.
>
> > len = _parse_integer(str, 10, &n);
> > if (!len)
> > return ERR_PTR(-EINVAL);
>
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
next prev parent reply other threads:[~2021-01-27 8:24 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 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-01-26 21:37 ` Andy Shevchenko
2021-01-26 21:41 ` Andy Shevchenko
2021-01-27 17:57 ` Yury Norov
2021-01-27 8:20 ` Paul Gortmaker [this message]
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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