On 10/24/2015 07:43 AM, Helge Deller wrote:
* Alexander Duyck <alexander.du...@gmail.com>:
On 10/23/2015 03:17 PM, Helge Deller wrote:
On 24.10.2015 00:00, Alexander Duyck wrote:
On 10/23/2015 02:08 PM, Helge Deller wrote:
* Eric Dumazet <eric.duma...@gmail.com>:
On Fri, 2015-10-23 at 21:25 +0200, Helge Deller wrote:

Then, how about simply changing it to twice of L1_CACHE_BYTES ?

#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES * 2 - sizeof(struct xps_map)) / 
sizeof(u16))


Seems good to me.

Great!

Can you then maybe give me an Acked-by or signed-off for the patch below?
It further adds a compile-time check to avoid that XPS_MIN_MAP_ALLOC
gets calculated to zero on any architecture - otherwise no queues would
be allocated.

In addition I would like to push it for v4.3 then through my parisc-tree
(after keeping it in for-next for 1-2 days), together with the patch
which reduces L1_CACHE_BYTES to 16 on parisc.
Would that be OK too?

Thanks!
Helge


[PATCH] net/xps: Increase initial number of xps queues

Increase the number of initial allocated xps queues, so that the initial record
allocates twice the size of L1_CACHE_BYTES bytes.

This change is needed to copy with architectures where L1_CACHE_BYTES is
defined to equal or less than 16 bytes.

Signed-off-by: Helge Deller <del...@gmx.de>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 2d15e38..d152788 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -718,7 +718,7 @@ struct xps_map {
       u16 queues[0];
   };
   #define XPS_MAP_SIZE(_num) (sizeof(struct xps_map) + ((_num) * sizeof(u16)))
-#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - sizeof(struct xps_map))    \
+#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES * 2 - sizeof(struct xps_map)) \
       / sizeof(u16))

   /*
diff --git a/net/core/dev.c b/net/core/dev.c
index 6bb6470..f6d6dd1 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1972,6 +1972,8 @@ static struct xps_map *expand_xps_map(struct xps_map *map,
       int alloc_len = XPS_MIN_MAP_ALLOC;
       int i, pos;

+    BUILD_BUG_ON(XPS_MIN_MAP_ALLOC == 0);
+
       for (pos = 0; map && pos < map->len; pos++) {
           if (map->queues[pos] != index)
               continue;



Rather then leaving a potential bug you could probably rewrite the macro so 
that it will give you at least 1.

All you need to do is something like the following
#define XPS_MIN_MAP_ALLOC \
     ((L1_CACHE_ALIGN(offsetof(struct xps_map, queue[1])) - \
       sizeof(struct xps_map)) / sizeof(u16))

That should give you at least an XPS_MIN_MAP_ALLOC of 1.

Yes, good idea!

What makes me wonder though (because I have no idea about the XPS code/layer):
How likely is it, that more than 1 (e.g. minimum "X") queues are needed?
E.g. if a typical system needs at least 3 queues, then doesn't it make sense to 
allocate
at least 3 initially by using queue[3] in your proposed patch above ?
What would "X" be then?

The question I would have is in how many cases it it likely that somebody
would enable this feature and point a given CPU at more than one queue.  I
know the Intel drivers that make use of XPS tend to do a 1:1 mapping for
their ATR feature.  I would think if anything most CPUs would probably be
mapped many:1, but you probably won't have all that many cases where it is
1:many or many:many.

I'd say starting with at least 1 should be fine.  Worst case scenario is we
have to make a couple more calls to expand_xps_map which will likely occur
as a slow path and infrequent event anyway.

Ok, can I get then the signed-off or acked-by from you for this patch?

Thanks,
Helge


[PATCH] net/xps: Fix calculation of initial number of xps queues

The existing code breaks on architectures where the L1 cache size
(L1_CACHE_BYTES) is smaller or equal the size of struct xps_map.

The new code ensures that we get at minimum one initial xps queue, or
even more as long as it fits into the next multiple of L1_CACHE_SIZE.

Signed-off-by: Helge Deller <del...@gmx.de>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 2d15e38..2212c82 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -718,8 +718,8 @@ struct xps_map {
        u16 queues[0];
  };
  #define XPS_MAP_SIZE(_num) (sizeof(struct xps_map) + ((_num) * sizeof(u16)))
-#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - sizeof(struct xps_map))   \
-    / sizeof(u16))
+#define XPS_MIN_MAP_ALLOC ((L1_CACHE_ALIGN(offsetof(struct xps_map, 
queues[1])) \
+       - sizeof(struct xps_map)) / sizeof(u16))

  /*
   * This structure holds all XPS maps for device.  Maps are indexed by CPU.


This looks good to me.

Acked-by: Alexander Duyck <adu...@mirantis.com>
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