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The users of RSS shouldn't be directly concerned about hash -> CPU ID

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mappings.  Instead, they should be first mapping to an RSS bucket and
then querying the RSS bucket -> CPU ID mapping to figure out the target
CPU.

When (if?) RSS rebalancing is implemented or some other (non round-robin)
distribution of work from buckets to CPU IDs, various bits of code - both
userland and kernel - will need to know how this mapping works.

So, to support this:

* Add a new function rss_m2bucket() - this maps an mbuf to a given bucket.
  Anything which is currently doing hash -> CPU work may instead wish to
  do hash -> bucket, and then query the bucket->cpuid map for which
  CPU it belongs on.  Or, map it to a bucket, then re-pin that bucket ->
  CPU during a rebalance operation.

* For userland applications which wish to exploit affinity to RSS buckets,
  the bucket -> CPU ID mapping is now available via a sysctl.
  net.inet.rss.bucket_mapping lists the bucket to CPU ID mapping via
  a list of bucket:cpu pairs.
This commit is contained in:
Adrian Chadd 2014-05-27 08:06:20 +00:00
parent b924fc0363
commit 8bde802a2b
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=266737
2 changed files with 60 additions and 0 deletions
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57
sys/netinet/in_rss.c
View File

@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
#include <sys/kernel.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/sbuf.h>
#include <net/if.h>
#include <net/if_var.h>
@ -424,6 +425,24 @@ rss_hash2cpuid(uint32_t hash_val, uint32_t hash_type)
}
}
/*
* Query the RSS bucket associated with the given hash value and
* type.
*/
int
rss_hash2bucket(uint32_t hash_val, uint32_t hash_type, uint32_t *bucket_id)
{
switch (hash_type) {
case M_HASHTYPE_RSS_IPV4:
case M_HASHTYPE_RSS_TCP_IPV4:
*bucket_id = rss_getbucket(hash_val);
return (0);
default:
return (-1);
}
}
/*
* netisr CPU affinity lookup routine for use by protocols.
*/
@ -436,6 +455,16 @@ rss_m2cpuid(struct mbuf *m, uintptr_t source, u_int *cpuid)
return (m);
}
int
rss_m2bucket(struct mbuf *m, uint32_t *bucket_id)
{
M_ASSERTPKTHDR(m);
return(rss_hash2bucket(m->m_pkthdr.flowid, M_HASHTYPE_GET(m),
bucket_id));
}
/*
* Query the RSS hash algorithm.
*/
@ -512,3 +541,31 @@ sysctl_rss_key(SYSCTL_HANDLER_ARGS)
SYSCTL_PROC(_net_inet_rss, OID_AUTO, key,
CTLTYPE_OPAQUE | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0, sysctl_rss_key,
"", "RSS keying material");
static int
sysctl_rss_bucket_mapping(SYSCTL_HANDLER_ARGS)
{
struct sbuf *sb;
int error;
int i;
error = 0;
error = sysctl_wire_old_buffer(req, 0);
if (error != 0)
return (error);
sb = sbuf_new_for_sysctl(NULL, NULL, 512, req);
if (sb == NULL)
return (ENOMEM);
for (i = 0; i < rss_buckets; i++) {
sbuf_printf(sb, "%s%d:%d", i == 0 ? "" : " ",
i,
rss_getcpu(i));
}
error = sbuf_finish(sb);
sbuf_delete(sb);
return (error);
}
SYSCTL_PROC(_net_inet_rss, OID_AUTO, bucket_mapping,
CTLTYPE_STRING | CTLFLAG_RD, NULL, 0,
sysctl_rss_bucket_mapping, "", "RSS bucket -> CPU mapping");

3
sys/netinet/in_rss.h
View File

@ -91,5 +91,8 @@ uint32_t rss_hash_ip6_2tuple(struct in6_addr src,
*/
struct mbuf *rss_m2cpuid(struct mbuf *m, uintptr_t source, u_int *cpuid);
u_int rss_hash2cpuid(uint32_t hash_val, uint32_t hash_type);
int rss_hash2bucket(uint32_t hash_val, uint32_t hash_type,
uint32_t *bucket_id);
int rss_m2bucket(struct mbuf *m, uint32_t *bucket_id);
#endif /* !_NETINET_IN_RSS_H_ */