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.
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
