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.dumazet@xxxxxxxxx>:
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 <deller@xxxxxx>
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.
- Alex
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