Messages in this thread | | | Date | Tue, 14 Jun 2022 08:42:34 +0800 | From | Feng Tang <> | Subject | Re: [tcp] e926147618: stress-ng.icmp-flood.ops_per_sec -8.7% regression |
| |
On Mon, Jun 13, 2022 at 10:10:57AM -0700, Eric Dumazet wrote: > On Sun, Jun 12, 2022 at 7:09 PM Feng Tang <feng.tang@intel.com> wrote: > > > > Hi, > > > > On Wed, Jun 08, 2022 at 09:34:41AM +0200, Willy Tarreau wrote: > > > On Wed, Jun 08, 2022 at 10:26:12AM +0300, Moshe Kol wrote: > > > > Hmm, How is the ICMP flood stress test related to TCP connections? > > > > > > To me it's not directly related, unless the test pre-establishes many > > > connections, or is affected in a way or another by a larger memory > > > allocation of this part. > > > > Fengwei and I discussed and thought this could be a data alignment > > related case, that one module's data alignment change affects other > > modules' alignment, and we had a patch for detecting similar cases [1] > > > > After some debugging, this could be related with the bss section > > alignment changes, that if we forced all module's bss section to be > > 4KB aligned, then the stress-ng icmp-flood case will have almost no > > performance difference for the 2 commits: > > > > 10025135 +0.8% 10105711 ± 2% stress-ng.icmp-flood.ops_per_sec > > > > The debug patch is: > > > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > > index 7fda7f27e7620..7eb626b98620c 100644 > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -378,7 +378,9 @@ SECTIONS > > > > /* BSS */ > > . = ALIGN(PAGE_SIZE); > > - .bss : AT(ADDR(.bss) - LOAD_OFFSET) { > > + .bss : AT(ADDR(.bss) - LOAD_OFFSET) > > + SUBALIGN(PAGE_SIZE) > > + { > > __bss_start = .; > > *(.bss..page_aligned) > > . = ALIGN(PAGE_SIZE); > > > > The 'table_perturb[]' used to be in bss section, and with the commit > > of moving it to runtime allocation, other data structures following it > > in the .bss section will get affected accordingly. > > > > As the 'regression' is seen with ICMP workload, can you please share with us > the symbols close to icmp_global (without your align patch)
Here are the info for the 2 commits (kernels for the original reprot):
$ egrep -8 "icmp_global$" System.map-5.18.0-rc4-00242-gca7af0402550 ffffffff837adc00 b tcp_cong_list_lock ffffffff837adc08 b tcpmhash_entries ffffffff837adc10 b fastopen_seqlock ffffffff837adc18 b tcp_metrics_lock ffffffff837adc1c b tcp_ulp_list_lock ffffffff837adc20 B raw_v4_hashinfo ffffffff837ae440 B udp_encap_needed_key ffffffff837ae480 B udp_memory_allocated ffffffff837ae488 b icmp_global ffffffff837ae4a0 b inet_addr_lst ffffffff837aeca0 b inetsw_lock ffffffff837aecc0 b inetsw ffffffff837aed80 b fib_info_devhash ffffffff837af580 b fib_info_cnt ffffffff837af584 b fib_info_hash_bits ffffffff837af588 b fib_info_hash_size ffffffff837af590 b fib_info_laddrhash
$ egrep -8 "icmp_global$" System.map-5.18.0-rc4-00243-ge9261476184b ffffffff837ad800 b tcp_cong_list_lock ffffffff837ad808 b tcpmhash_entries ffffffff837ad810 b fastopen_seqlock ffffffff837ad818 b tcp_metrics_lock ffffffff837ad81c b tcp_ulp_list_lock ffffffff837ad820 B raw_v4_hashinfo ffffffff837ae040 B udp_encap_needed_key ffffffff837ae080 B udp_memory_allocated ffffffff837ae088 b icmp_global ffffffff837ae0a0 b inet_addr_lst ffffffff837ae8a0 b inetsw_lock ffffffff837ae8c0 b inetsw ffffffff837ae980 b fib_info_devhash ffffffff837af180 b fib_info_cnt ffffffff837af184 b fib_info_hash_bits ffffffff837af188 b fib_info_hash_size ffffffff837af190 b fib_info_laddrhash
From above we can see some symbols are offseted of 0x400 (1KB), like icmp_global or fib_xxx, as the 'table_perturb' used to be 1KB long in bss section.
> I suspect we should move icmp_global to a dedicated cache line. > > $ nm -v vmlinux|egrep -8 "icmp_global$" > ffffffff835bc490 b tcp_cong_list_lock > ffffffff835bc494 b fastopen_seqlock > ffffffff835bc49c b tcp_metrics_lock > ffffffff835bc4a0 b tcpmhash_entries > ffffffff835bc4a4 b tcp_ulp_list_lock > ffffffff835bc4a8 B raw_v4_hashinfo > ffffffff835bccc0 B udp_memory_allocated << Note sure why it is > not already in a dedicated cache line>>
IIUC, 0x....C0 means it is already cacheline aligned?
> ffffffff835bccc8 B udp_encap_needed_key > ffffffff835bccd8 b icmp_global <<<HERE>> > ffffffff835bccf0 b inet_addr_lst > ffffffff835bd4f0 b inetsw_lock > ffffffff835bd500 b inetsw > ffffffff835bd5b0 b fib_info_lock > ffffffff835bd5b4 b fib_info_cnt > ffffffff835bd5b8 b fib_info_hash_size > ffffffff835bd5c0 b fib_info_hash > ffffffff835bd5c8 b fib_info_laddrhash
Fengwei found that from the perf-profile info of report, there are quite difference around ping table handling.
43.72 +4.1 47.81 ± 2% icmp_rcv.ip_protocol_deliver_rcu.ip_local_deliver_finish.__netif_receive_skb_one_core.process_backlog 17.10 ± 7% +6.0 23.10 ± 6%ping_rcv.icmp_rcv.ip_protocol_deliver_rcu.ip_local_deliver_finish.__netif_receive_skb_one_core 17.05 ± 7% +6.0 23.06 ± 6%ping_lookup.ping_rcv.icmp_rcv.ip_protocol_deliver_rcu.ip_local_deliver_finish
And the "ping_table[]" also sits in bss section and got affected:
Before: ffffffff837af600 b ping_table
After: ffffffff837af200 b ping_table
The cacheline alignment is not changed, and I suspect it cause some TLB changes.
Thanks, Feng
| |