Commit 2d13e6ca authored by Noam Camus's avatar Noam Camus Committed by Linus Torvalds
Browse files

lib/bitmap.c: enhance bitmap syntax 

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>:sed_size/group_size

For example, above map can be described in new syntax like this:
0-4095:8/16

Note that this patch is backward compatible with current syntax.

[akpm@linux-foundation.org: rework documentation]
Link: http://lkml.kernel.org/r/1473579629-4283-1-git-send-email-noamca@mellanox.com


Signed-off-by: default avatarNoam Camus <noamca@mellanox.com>
Cc: David Decotigny <decot@googlers.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: David S. Miller <davem@davemloft.net>
Cc: Pan Xinhui <xinhui@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8cfd56d4

Documentation/kernel-parameters.txt

+36 −14
Original line number Diff line number Diff line
@@ -33,6 +33,37 @@ can also be entered as 
Double-quotes can be used to protect spaces in values, e.g.:

	param="spaces in here"



cpu lists:

----------



Some kernel parameters take a list of CPUs as a value, e.g.  isolcpus,

nohz_full, irqaffinity, rcu_nocbs.  The format of this list is:



	<cpu number>,...,<cpu number>



or



	<cpu number>-<cpu number>

	(must be a positive range in ascending order)



or a mixture



<cpu number>,...,<cpu number>-<cpu number>



Note that for the special case of a range one can split the range into equal

sized groups and for each group use some amount from the beginning of that

group:



	<cpu number>-cpu number>:<used size>/<group size>



For example one can add to the command line following parameter:



	isolcpus=1,2,10-20,100-2000:2/25



where the final item represents CPUs 100,101,125,126,150,151,...







This document may not be entirely up to date and comprehensive. The command

"modinfo -p ${modulename}" shows a current list of all parameters of a loadable

module. Loadable modules, after being loaded into the running kernel, also
@@ -1789,13 +1820,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			See Documentation/filesystems/nfs/nfsroot.txt.



	irqaffinity=	[SMP] Set the default irq affinity mask

			Format:

			<cpu number>,...,<cpu number>

			or

			<cpu number>-<cpu number>

			(must be a positive range in ascending order)

			or a mixture

			<cpu number>,...,<cpu number>-<cpu number>

			The argument is a cpu list, as described above.



	irqfixup	[HW]

			When an interrupt is not handled search all handlers
@@ -1812,13 +1837,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Format: <RDP>,<reset>,<pci_scan>,<verbosity>



	isolcpus=	[KNL,SMP] Isolate CPUs from the general scheduler.

			Format:

			<cpu number>,...,<cpu number>

			or

			<cpu number>-<cpu number>

			(must be a positive range in ascending order)

			or a mixture

			<cpu number>,...,<cpu number>-<cpu number>

			The argument is a cpu list, as described above.



			This option can be used to specify one or more CPUs

			to isolate from the general SMP balancing and scheduling
@@ -2680,6 +2699,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Default: on



	nohz_full=	[KNL,BOOT]

			The argument is a cpu list, as described above.

			In kernels built with CONFIG_NO_HZ_FULL=y, set

			the specified list of CPUs whose tick will be stopped

			whenever possible. The boot CPU will be forced outside
@@ -3285,6 +3305,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			See Documentation/blockdev/ramdisk.txt.



	rcu_nocbs=	[KNL]

			The argument is a cpu list, as described above.



			In kernels built with CONFIG_RCU_NOCB_CPU=y, set

			the specified list of CPUs to be no-callback CPUs.

			Invocation of these CPUs' RCU callbacks will

lib/bitmap.c

+46 −4
Original line number Diff line number Diff line
@@ -496,6 +496,11 @@ 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 range will divided to groups of specific size.

 * From each group will be used only defined amount of bits.

 * Syntax: range:used_size/group_size

 * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769

 *

 * Returns 0 on success, -errno on invalid input strings.

 * Error values:
@@ -507,16 +512,20 @@ 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;

	unsigned int group_size, used_size;

	int c, old_c, totaldigits, ndigits;

	const char __user __force *ubuf = (const char __user __force *)buf;

	int at_start, in_range;

	int at_start, in_range, in_partial_range;



	totaldigits = c = 0;

	old_a = old_b = 0;

	group_size = used_size = 0;

	bitmap_zero(maskp, nmaskbits);

	do {

		at_start = 1;

		in_range = 0;

		in_partial_range = 0;

		a = b = 0;

		ndigits = totaldigits;
@@ -547,6 +556,24 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen, 
			if ((totaldigits != ndigits) && isspace(old_c))

				return -EINVAL;



			if (c == '/') {

				used_size = 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;

				in_partial_range = 1;

				a = b = 0;

				continue;

			}



			if (c == '-') {

				if (at_start || in_range)

					return -EINVAL;
@@ -567,14 +594,29 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen, 
		}

		if (ndigits == totaldigits)

			continue;

		if (in_partial_range) {

			group_size = a;

			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) || !(used_size <= group_size))

			return -EINVAL;

		if (b >= nmaskbits)

			return -ERANGE;

		while (a <= b) {

			if (in_partial_range) {

				static int pos_in_group = 1;



				if (pos_in_group <= used_size)

					set_bit(a, maskp);



				if (a == b || ++pos_in_group > group_size)

					pos_in_group = 1;

			} else

				set_bit(a, maskp);

			a++;

		}

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