Messages in this thread | | | Date | Tue, 18 Jul 2023 15:50:08 +0200 | Subject | Re: [PATCH RFC net-next v2 2/7] net: page_pool: place frag_* fields in one cacheline | From | Alexander Lobakin <> |
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From: Jesper Dangaard Brouer <jbrouer@redhat.com> Date: Fri, 14 Jul 2023 20:37:39 +0200
> > > On 14/07/2023 19.08, Alexander Lobakin wrote: >> On x86_64, frag_* fields of struct page_pool are scattered across two >> cachelines despite the summary size of 24 bytes. The last field, >> ::frag_users, is pushed out to the next one, sharing it with >> ::alloc_stats. >> All three fields are used in pretty much the same places. There are some >> holes and cold members to move around. Move frag_* one block up, placing >> them right after &page_pool_params perfectly at the beginning of CL2. >> This doesn't do any meaningful to the second block, as those are some >> destroy-path cold structures, and doesn't do anything to ::alloc_stats, >> which still starts at 200-byte offset, 8 bytes after CL3 (still fitting >> into 1 cacheline). >> On my setup, this yields 1-2% of Mpps when using PP frags actively. >> When it comes to 32-bit architectures with 32-byte CL: &page_pool_params >> plus ::pad is 44 bytes, the block taken care of is 16 bytes within one >> CL, so there should be at least no regressions from the actual change. >> >> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> >> --- >> include/net/page_pool.h | 10 +++++----- >> 1 file changed, 5 insertions(+), 5 deletions(-) >> >> diff --git a/include/net/page_pool.h b/include/net/page_pool.h >> index 829dc1f8ba6b..212d72b5cfec 100644 >> --- a/include/net/page_pool.h >> +++ b/include/net/page_pool.h >> @@ -130,16 +130,16 @@ static inline u64 >> *page_pool_ethtool_stats_get(u64 *data, void *stats) >> struct page_pool { >> struct page_pool_params p; >> + long frag_users; >> + struct page *frag_page; >> + unsigned int frag_offset; >> + u32 pages_state_hold_cnt; > > I think this is okay, but I want to highlight that: > - pages_state_hold_cnt and pages_state_release_cnt > need to be kept on separate cache-lines.
They're pretty far away from each other. I moved hold_cnt here as well to keep it stacked with frag_offset and avoid introducing 32-bit holes.
> > >> + >> struct delayed_work release_dw; >> void (*disconnect)(void *); >> unsigned long defer_start; >> unsigned long defer_warn; >> - u32 pages_state_hold_cnt; >> - unsigned int frag_offset; >> - struct page *frag_page; >> - long frag_users; >> - >> #ifdef CONFIG_PAGE_POOL_STATS >> /* these stats are incremented while in softirq context */ >> struct page_pool_alloc_stats alloc_stats; >
Thanks, Olek
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