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Some cache related optimizations

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1. prefetch 128 bytes of mbufs.
2. Re-order filling the pkt_info so cache stalls happen at the end
3. Define empty prefetch2cachelines() macro when the function isn't present.

Provides small performance improvments on some hardware

Reviewed by:	sbruno
Approved by:	sbruno (mentor)
Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D12447
This commit is contained in:
Stephen Hurd 2017-10-23 20:50:08 +00:00
parent aa86fca1d1
commit 3429c02f82
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=324937
1 changed files with 16 additions and 7 deletions
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23
sys/net/iflib.c
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@ -1227,8 +1227,17 @@ prefetch(void *x)
{
__asm volatile("prefetcht0 %0" :: "m" (*(unsigned long *)x));
}
static __inline void
prefetch2cachelines(void *x)
{
__asm volatile("prefetcht0 %0" :: "m" (*(unsigned long *)x));
#if (CACHE_LINE_SIZE < 128)
__asm volatile("prefetcht0 %0" :: "m" (*(((unsigned long *)x)+CACHE_LINE_SIZE/(sizeof(unsigned long)))));
#endif
}
#else
#define prefetch(x)
#define prefetch2cachelines(x)
#endif
static void
@ -3086,12 +3095,12 @@ iflib_encap(iflib_txq_t txq, struct mbuf **m_headp)
m_head = *m_headp;
pkt_info_zero(&pi);
pi.ipi_len = m_head->m_pkthdr.len;
pi.ipi_mflags = (m_head->m_flags & (M_VLANTAG|M_BCAST|M_MCAST));
pi.ipi_csum_flags = m_head->m_pkthdr.csum_flags;
pi.ipi_vtag = (m_head->m_flags & M_VLANTAG) ? m_head->m_pkthdr.ether_vtag : 0;
pi.ipi_pidx = pidx;
pi.ipi_qsidx = txq->ift_id;
pi.ipi_len = m_head->m_pkthdr.len;
pi.ipi_csum_flags = m_head->m_pkthdr.csum_flags;
pi.ipi_vtag = (m_head->m_flags & M_VLANTAG) ? m_head->m_pkthdr.ether_vtag : 0;
/* deliberate bitwise OR to make one condition */
if (__predict_true((pi.ipi_csum_flags | pi.ipi_vtag))) {
@ -3323,10 +3332,10 @@ _ring_peek_one(struct ifmp_ring *r, int cidx, int offset, int remaining)
prefetch(items[(cidx + offset) & (size-1)]);
if (remaining > 1) {
prefetch(&items[next]);
prefetch(items[(cidx + offset + 1) & (size-1)]);
prefetch(items[(cidx + offset + 2) & (size-1)]);
prefetch(items[(cidx + offset + 3) & (size-1)]);
prefetch2cachelines(&items[next]);
prefetch2cachelines(items[(cidx + offset + 1) & (size-1)]);
prefetch2cachelines(items[(cidx + offset + 2) & (size-1)]);
prefetch2cachelines(items[(cidx + offset + 3) & (size-1)]);
}
return (__DEVOLATILE(struct mbuf **, &r->items[(cidx + offset) & (size-1)]));
}