linux-kernel - Re: [PATCH v3] lib/bitmap.c: enhance bitmap syntax

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Message-Id: <06d3f797-2de6-42a2-c356-db086e14836c@linux.vnet.ibm.com>
Date:	Sun, 17 Jul 2016 21:59:21 +0800
From:	Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:	Noam Camus <noamca@...lanox.com>, decot@...glers.com
Cc:	ben@...adent.org.uk, davem@...emloft.net,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] lib/bitmap.c: enhance bitmap syntax



在 16/7/17 21:50, Pan Xinhui 写道:
>
>
> 在 16/7/17 16:10, Noam Camus 写道:
>> From: Noam Camus <noamca@...lanox.com>
>>
>> Today there are platforms with many CPUs (up to 4K).
>> Trying to boot only part of the CPUs may result in too long string.
>>
>> For example lets take NPS platform that is part of arch/arc.
>> This platform have SMP system with 256 cores each with
>> 16 HW threads (SMT machine) where HW thread appears as CPU to the kernel.
>> In this example there is total of 4K CPUs.
>> When one tries to boot only part of the HW threads from each core the
>> string representing the map may be long...
>> For example if for sake of performance we decided to boot only first half
>> of HW threads of each core the map will look like:
>> 0-7,16-23,32-39,...,4080-4087
>>
>> This patch introduce new syntax to accommodate with such use case.
>> I added an optional postfix to a range of CPUs which will choose
>> according to given modulo the desired range of reminders i.e.:
>>     <cpus range>%modulo=<range of reminders>
>>
>> For example, above map can be described in new syntax like this:
>> 0-4095%16=0-7
>>
>
> I really think it is better to implement one function to generic a string which contanis the cpus you want to boot on, then pass this string to  __bitmap_parselist.
>
sorry, typos.
generic -> generate.

>> Note that this patch is backward compatible with current syntax.
>>
>> Signed-off-by: Noam Camus <noamca@...lanox.com>
>> ---
>> Any sugestions for simpler syntax which keeps its generality are welcomed.
>>
>> Change Log:
>> V2: Fix typo in example at function header for __bitmap_parselist()
>> V3: Fix typo in commit log and also typo at example
>> ---
>>  lib/bitmap.c |   44 ++++++++++++++++++++++++++++++++++++++++----
>>  1 files changed, 40 insertions(+), 4 deletions(-)
>>
>> diff --git a/lib/bitmap.c b/lib/bitmap.c
>> index c66da50..bccfd87 100644
>> --- a/lib/bitmap.c
>> +++ b/lib/bitmap.c
>> @@ -496,6 +496,9 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf);
>>   * ranges.  Consecutively set bits are shown as two hyphen-separated
>>   * decimal numbers, the smallest and largest bit numbers set in
>>   * the range.
>> + * Optionally each range can be postfixed to denote that only parts of it
>> + * should be set. The parts are the range of reminders modulo some value.
>> + * i.e. range%mod=rem_range e.g. 0-1023%256=0-1 ==> 0,1,256,257,512,513,768,769
>>   *
>>   * Returns 0 on success, -errno on invalid input strings.
>>   * Error values:
>> @@ -507,12 +510,14 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>>          int is_user, unsigned long *maskp,
>>          int nmaskbits)
>>  {
>> -    unsigned a, b;
>> +    unsigned int a, b, old_a, old_b, mod_val, mod_a, mod_b;
>>      int c, old_c, totaldigits, ndigits;
>>      const char __user __force *ubuf = (const char __user __force *)buf;
>>      int at_start, in_range;
>>
>>      totaldigits = c = 0;
>> +    old_a = old_b = 0;
>> +    mod_val = mod_a = mod_b = 0;
>>      bitmap_zero(maskp, nmaskbits);
>>      do {
>>          at_start = 1;
>> @@ -547,6 +552,23 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>>              if ((totaldigits != ndigits) && isspace(old_c))
>>                  return -EINVAL;
>>
>> +            if (c == '=') {
>> +                mod_val = a;
>> +                at_start = 1;
>> +                in_range = 0;
>> +                a = b = 0;
>> +                continue;
>> +            }
>> +
>> +            if (c == '%') {
>> +                old_a = a;
>> +                old_b = b;
>> +                at_start = 1;
>> +                in_range = 0;
>> +                a = b = 0;
>> +                continue;
>> +            }
>> +
>>              if (c == '-') {
>>                  if (at_start || in_range)
>>                      return -EINVAL;
>> @@ -567,17 +589,31 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
>>          }
>>          if (ndigits == totaldigits)
>>              continue;
>> +        if (mod_val) {
>> +            mod_a = a;
>> +            mod_b = b;
>> +            a = old_a;
>> +            b = old_b;
>> +            old_a = old_b = 0;
>> +        }
>>          /* if no digit is after '-', it's wrong*/
>>          if (at_start && in_range)
>>              return -EINVAL;
>> -        if (!(a <= b))
>> +        if (!(a <= b) || !(mod_a <= mod_b))
>>              return -EINVAL;
>> -        if (b >= nmaskbits)
>> +        if (b >= nmaskbits || (mod_val && (mod_b >= mod_val)))
>>              return -ERANGE;
>>          while (a <= b) {
>> -            set_bit(a, maskp);
>> +            if (mod_val) {
>> +                unsigned int rem = a % mod_val;
>> +
>> +                if (rem >= mod_a && rem <= mod_b)
>> +                    set_bit(a, maskp);
>> +            } else
>> +                set_bit(a, maskp);
>>              a++;
>>          }
>> +        mod_val = mod_a = mod_b = 0;
>>      } while (buflen && c == ',');
>>      return 0;
>>  }
>>