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SubjectRe: [PATCH RFC/RFT v3 2/9] drivers: base: support cpu cache information interface to userspace via sysfs
On Wed, Feb 19, 2014 at 04:06:09PM +0000, Sudeep Holla wrote:
> From: Sudeep Holla <sudeep.holla@arm.com>
>
> This patch adds initial support for providing processor cache information
> to userspace through sysfs interface. This is based on already existing
> implementations(x86, ia64, s390 and powerpc) and hence the interface is
> intended to be fully compatible.
>
> The main purpose of this generic support is to avoid further code
> duplication to support new architectures and also to unify all the existing
> different implementations.
>
> This implementation maintains the hierarchy of cache objects which reflects
> the system's cache topology. Cache devices are instantiated as needed as
> CPUs come online. The cache information is replicated per-cpu even if they are
> shared. A per-cpu array of cache information maintained is used mainly for
> sysfs-related book keeping.
>
> It also implements the shared_cpu_map attribute, which is essential for
> enabling both kernel and user-space to discover the system's overall cache
> topology.
>
> This patch also add the missing ABI documentation for the cacheinfo sysfs
> interface already, which is well defined and widely used.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: linux-doc@vger.kernel.org
> ---
> Documentation/ABI/testing/sysfs-devices-system-cpu | 40 ++
> drivers/base/Makefile | 2 +-
> drivers/base/cacheinfo.c | 484 +++++++++++++++++++++
> include/linux/cacheinfo.h | 55 +++
> 4 files changed, 580 insertions(+), 1 deletion(-)
> create mode 100644 drivers/base/cacheinfo.c
> create mode 100644 include/linux/cacheinfo.h
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index d5a0d33..dabe03e 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -224,3 +224,43 @@ Description: Parameters for the Intel P-state driver
> frequency range.
>
> More details can be found in Documentation/cpu-freq/intel-pstate.txt
> +
> +What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
> +Date: February 2014
> +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>

No, your name goes here, you don't get to run away from this new code :)

> +Description: Parameters for the CPU cache attributes
> +
> + attributes:
> + - writethrough: data is written to both the cache line
> + and to the block in the lower-level memory
> + - writeback: data is written only to the cache line and
> + the modified cache line is written to main
> + memory only when it is replaced
> + - writeallocate: allocate a memory location to a cache line
> + on a cache miss because of a write
> + - readallocate: allocate a memory location to a cache line
> + on a cache miss because of a read
> +
> + coherency_line_size: the minimum amount of data that gets transferred
> +
> + level: the cache hierarcy in the multi-level cache configuration
> +
> + number_of_sets: total number of sets in the cache, a set is a
> + collection of cache lines with the same cache index
> +
> + physical_line_partition: number of physical cache line per cache tag
> +
> + shared_cpu_list: the list of cpus sharing the cache
> +
> + shared_cpu_map: logical cpu mask containing the list of cpus sharing
> + the cache
> +
> + size: the total cache size in kB
> +
> + type:
> + - instruction: cache that only holds instructions
> + - data: cache that only caches data
> + - unified: cache that holds both data and instructions
> +
> + ways_of_associativity: degree of freedom in placing a particular block
> + of memory in the cache

With this patch, does this all work for x86, or does it need more glue
logic?
thanks,

greg k-h


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