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

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Date:	Sun, 17 Jul 2016 21:50:15 +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 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.

> 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;
>  }
>