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In mb_dupcl() don't copy full m_ext, to avoid cache miss. Respectively,

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in mb_free_ext() always use fields from the original refcount holding
mbuf (see. r296242) mbuf.  Cuts another cache miss from mb_free_ext().

However, treat EXT_EXTREF mbufs differently, since they are different -
they don't have a refcount holding mbuf.

Provide longer comments in m_ext declaration to explain this change
and change from r296242.

In collaboration with:	gallatin
Differential Revision:	https://reviews.freebsd.org/D12615
This commit is contained in:
Gleb Smirnoff 2017-10-09 20:51:58 +00:00
parent e8fd18f306
commit 07e87a1d55
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=324447
3 changed files with 34 additions and 8 deletions
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10
sys/kern/kern_mbuf.c
View File

@ -675,20 +675,20 @@ mb_free_ext(struct mbuf *m)
uma_zfree(zone_mbuf, mref);
break;
case EXT_SFBUF:
sf_ext_free(m->m_ext.ext_arg1, m->m_ext.ext_arg2);
sf_ext_free(mref->m_ext.ext_arg1, mref->m_ext.ext_arg2);
uma_zfree(zone_mbuf, mref);
break;
case EXT_SFBUF_NOCACHE:
sf_ext_free_nocache(m->m_ext.ext_arg1,
m->m_ext.ext_arg2);
sf_ext_free_nocache(mref->m_ext.ext_arg1,
mref->m_ext.ext_arg2);
uma_zfree(zone_mbuf, mref);
break;
case EXT_NET_DRV:
case EXT_MOD_TYPE:
case EXT_DISPOSABLE:
KASSERT(m->m_ext.ext_free != NULL,
KASSERT(mref->m_ext.ext_free != NULL,
("%s: ext_free not set", __func__));
m->m_ext.ext_free(m);
mref->m_ext.ext_free(mref);
uma_zfree(zone_mbuf, mref);
break;
case EXT_EXTREF:

12
sys/kern/uipc_mbuf.c
View File

@ -188,7 +188,17 @@ mb_dupcl(struct mbuf *n, struct mbuf *m)
KASSERT(m->m_flags & M_EXT, ("%s: M_EXT not set on %p", __func__, m));
KASSERT(!(n->m_flags & M_EXT), ("%s: M_EXT set on %p", __func__, n));
n->m_ext = m->m_ext;
/*
* Cache access optimization. For most kinds of external
* storage we don't need full copy of m_ext, since the
* holder of the 'ext_count' is responsible to carry the
* free routine and its arguments. Exclusion is EXT_EXTREF,
* where 'ext_cnt' doesn't point into mbuf at all.
*/
if (m->m_ext.ext_type == EXT_EXTREF)
bcopy(&m->m_ext, &n->m_ext, sizeof(struct m_ext));
else
bcopy(&m->m_ext, &n->m_ext, m_ext_copylen);
n->m_flags |= M_EXT;
n->m_flags |= m->m_flags & M_RDONLY;

20
sys/sys/mbuf.h
View File

@ -200,13 +200,29 @@ struct pkthdr {
typedef void m_ext_free_t(struct mbuf *);
struct m_ext {
union {
volatile u_int ext_count; /* value of ref count info */
volatile u_int *ext_cnt; /* pointer to ref count info */
/*
* If EXT_FLAG_EMBREF is set, then we use refcount in the
* mbuf, the 'ext_count' member. Otherwise, we have a
* shadow copy and we use pointer 'ext_cnt'. The original
* mbuf is responsible to carry the pointer to free routine
* and its arguments. They aren't copied into shadows in
* mb_dupcl() to avoid dereferencing next cachelines.
*/
volatile u_int ext_count;
volatile u_int *ext_cnt;
};
char *ext_buf; /* start of buffer */
uint32_t ext_size; /* size of buffer, for ext_free */
uint32_t ext_type:8, /* type of external storage */
ext_flags:24; /* external storage mbuf flags */
/*
* Fields below store the free context for the external storage.
* They are valid only in the refcount carrying mbuf, the one with
* EXT_FLAG_EMBREF flag, with exclusion for EXT_EXTREF type, where
* the free context is copied into all mbufs that use same external
* storage.
*/
#define m_ext_copylen offsetof(struct m_ext, ext_free)
m_ext_free_t *ext_free; /* free routine if not the usual */
void *ext_arg1; /* optional argument pointer */
void *ext_arg2; /* optional argument pointer */