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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
> 
> 

  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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