Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit a37e6e34 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: force dst_default_metrics to const section 



While investigating on network performance problems, I found this little
gem :

$ nm -v vmlinux | grep -1 dst_default_metrics
ffffffff82736540 b busy.46605
ffffffff82736560 B dst_default_metrics
ffffffff82736598 b dst_busy_list

Apparently, declaring a const array without initializer put it in
(writeable) bss section, in middle of possibly often dirtied cache
lines.

Since we really want dst_default_metrics be const to avoid any possible
false sharing and catch any buggy writes, I force a null initializer.

ffffffff818a4c20 R dst_default_metrics

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0c03eca3

include/net/dst.h

+1 −1
Original line number Diff line number Diff line
@@ -110,7 +110,7 @@ struct dst_entry { 
};



extern u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);

extern const u32 dst_default_metrics[RTAX_MAX];

extern const u32 dst_default_metrics[];



#define DST_METRICS_READ_ONLY	0x1UL

#define __DST_METRICS_PTR(Y)	\

net/core/dst.c

+9 −1
Original line number Diff line number Diff line
@@ -149,7 +149,15 @@ int dst_discard(struct sk_buff *skb) 
}

EXPORT_SYMBOL(dst_discard);



const u32 dst_default_metrics[RTAX_MAX];

const u32 dst_default_metrics[RTAX_MAX + 1] = {

	/* This initializer is needed to force linker to place this variable

	 * into const section. Otherwise it might end into bss section.

	 * We really want to avoid false sharing on this variable, and catch

	 * any writes on it.

	 */

	[RTAX_MAX] = 0xdeadbeef,

};





void *dst_alloc(struct dst_ops *ops, struct net_device *dev,

		int initial_ref, int initial_obsolete, unsigned short flags)