On 2022-05-31 19:17, Tony Battersby wrote:
> The "total number of blocks in pool" debug statistic currently does not
> take the boundary value into account, so it diverges from the "total
> number of blocks in use" statistic when a boundary is in effect. Add a
> calculation for the number of blocks per allocation that takes the
> boundary into account, and use it to replace the inaccurate calculation.
>
> This depends on the patch "dmapool: fix boundary comparison" for the
> calculated blks_per_alloc value to be correct.
>
> Signed-off-by: Tony Battersby <[email protected]>
> ---
> mm/dmapool.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/dmapool.c b/mm/dmapool.c
> index 782143144a32..9e30f4425dea 100644
> --- a/mm/dmapool.c
> +++ b/mm/dmapool.c
> @@ -47,6 +47,7 @@ struct dma_pool { /* the pool */
> struct device *dev;
> unsigned int allocation;
> unsigned int boundary;
> + unsigned int blks_per_alloc;
> char name[32];
> struct list_head pools;
> };
> @@ -92,8 +93,7 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
> /* per-pool info, no real statistics yet */
> temp = scnprintf(next, size, "%-16s %4zu %4zu %4u %2u\n",
Nit: if we're tinkering with this, it's probably worth updating the
whole function to use sysfs_emit{_at}().
> pool->name, blocks,
> - (size_t) pages *
> - (pool->allocation / pool->size),
> + (size_t) pages * pool->blks_per_alloc,
> pool->size, pages);
> size -= temp;
> next += temp;
> @@ -168,6 +168,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
> retval->size = size;
> retval->boundary = boundary;
> retval->allocation = allocation;
> + retval->blks_per_alloc =
> + (allocation / boundary) * (boundary / size) +
> + (allocation % boundary) / size;
Do we really need to store this? Sure, 4 divisions (which could possibly
be fewer given the constraints on boundary) isn't the absolute cheapest
calculation, but I still can't imagine anyone would be polling sysfs
stats hard enough to even notice.
Thanks,
Robin.
>
> INIT_LIST_HEAD(&retval->pools);
>
On 5/31/22 15:48, Robin Murphy wrote:
> On 2022-05-31 19:17, Tony Battersby wrote:
>
>> pool->name, blocks,
>> - (size_t) pages *
>> - (pool->allocation / pool->size),
>> + (size_t) pages * pool->blks_per_alloc,
>> pool->size, pages);
>> size -= temp;
>> next += temp;
>> @@ -168,6 +168,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
>> retval->size = size;
>> retval->boundary = boundary;
>> retval->allocation = allocation;
>> + retval->blks_per_alloc =
>> + (allocation / boundary) * (boundary / size) +
>> + (allocation % boundary) / size;
> Do we really need to store this? Sure, 4 divisions (which could possibly
> be fewer given the constraints on boundary) isn't the absolute cheapest
> calculation, but I still can't imagine anyone would be polling sysfs
> stats hard enough to even notice.
>
The stored value is also used in patch #5, in more performance-critical
code, although only when debug is enabled.
Tony