Subject: Re: CONFIG_XPS depends on L1_CACHE_BYTES being greater than sizeof(struct xps_map)

From: Helge Deller <[email-masked]>
Date: Fri, 23 Oct 2015 23:08:10 +0200

* Eric Dumazet <[email-masked]>:
> 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 <[email-masked]>

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;