RE: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper size

Zhang, Cathy
2023-05-11T09:27:36Z

> -----Original Message-----
> From: Eric Dumazet <edumazet@google.com>
> Sent: Thursday, May 11, 2023 3:51 PM
> To: Zhang, Cathy <cathy.zhang@intel.com>
> Cc: Shakeel Butt <shakeelb@google.com>; Linux MM <linux-mm@kvack.org>;
> Cgroups <cgroups@vger.kernel.org>; Paolo Abeni <pabeni@redhat.com>;
> davem@davemloft.net; kuba@kernel.org; Brandeburg, Jesse
> <jesse.brandeburg@intel.com>; Srinivas, Suresh
> <suresh.srinivas@intel.com>; Chen, Tim C <tim.c.chen@intel.com>; You,
> Lizhen <lizhen.you@intel.com>; eric.dumazet@gmail.com;
> netdev@vger.kernel.org
> Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper
> size
>
> On Thu, May 11, 2023 at 9:00 AM Zhang, Cathy <cathy.zhang@intel.com>
> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Zhang, Cathy
> > > Sent: Thursday, May 11, 2023 8:53 AM
> > > To: Shakeel Butt <shakeelb@google.com>
> > > Cc: Eric Dumazet <edumazet@google.com>; Linux MM <linux-
> > > mm@kvack.org>; Cgroups <cgroups@vger.kernel.org>; Paolo Abeni
> > > <pabeni@redhat.com>; davem@davemloft.net; kuba@kernel.org;
> > > Brandeburg, Jesse <jesse.brandeburg@intel.com>; Srinivas, Suresh
> > > <suresh.srinivas@intel.com>; Chen, Tim C <tim.c.chen@intel.com>;
> > > You, Lizhen <Lizhen.You@intel.com>; eric.dumazet@gmail.com;
> > > netdev@vger.kernel.org
> > > Subject: RE: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as
> > > a proper size
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Shakeel Butt <shakeelb@google.com>
> > > > Sent: Thursday, May 11, 2023 3:00 AM
> > > > To: Zhang, Cathy <cathy.zhang@intel.com>
> > > > Cc: Eric Dumazet <edumazet@google.com>; Linux MM <linux-
> > > > mm@kvack.org>; Cgroups <cgroups@vger.kernel.org>; Paolo Abeni
> > > > <pabeni@redhat.com>; davem@davemloft.net; kuba@kernel.org;
> > > Brandeburg,
> > > > Jesse <jesse.brandeburg@intel.com>; Srinivas, Suresh
> > > > <suresh.srinivas@intel.com>; Chen, Tim C <tim.c.chen@intel.com>;
> > > > You, Lizhen <lizhen.you@intel.com>; eric.dumazet@gmail.com;
> > > > netdev@vger.kernel.org
> > > > Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc
> > > > as a proper size
> > > >
> > > > On Wed, May 10, 2023 at 9:09 AM Zhang, Cathy
> > > > <cathy.zhang@intel.com>
> > > > wrote:
> > > > >
> > > > >
> > > > [...]
> > > > > > > >
> > > > > > > > Have you tried to increase batch sizes ?
> > > > > > >
> > > > > > > I jus picked up 256 and 1024 for a try, but no help, the
> > > > > > > overhead still
> > > > exists.
> > > > > >
> > > > > > This makes no sense at all.
> > > > >
> > > > > Eric,
> > > > >
> > > > > I added a pr_info in try_charge_memcg() to print nr_pages if
> > > > > nr_pages
> > > > > >= MEMCG_CHARGE_BATCH, except it prints 64 during the
> > > > > >initialization
> > > > > of instances, there is no other output during the running. That
> > > > > means nr_pages is not over 64, I guess that might be the reason
> > > > > why to increase MEMCG_CHARGE_BATCH doesn't affect this case.
> > > > >
> > > >
> > > > I am assuming you increased MEMCG_CHARGE_BATCH to 256 and 1024
> > > but
> > > > that did not help. To me that just means there is a different
> > > > bottleneck in the memcg charging codepath. Can you please share
> > > > the perf profile? Please note that memcg charging does a lot of
> > > > other things as well like updating memcg stats and checking (and
> > > > enforcing) memory.high even if you have not set memory.high.
> > >
> > > Thanks Shakeel! I will check more details on what you mentioned. We
> > > use "sudo perf top -p $(docker inspect -f '{{.State.Pid}}'
> > > memcached_2)" to monitor one of those instances, and also use "sudo
> > > perf top" to check the overhead from system wide.
> >
> > Here is the annotate output of perf top for the three memcg hot paths:
> >
> > Showing cycles for page_counter_try_charge
> > Events Pcnt (>=5%)
> > Percent | Source code & Disassembly of elf for cycles (543288 samples,
> percent: local period)
> > --------------------------------------------------------------------------------------------------
> -
> > 0.00 : ffffffff8141388d: mov %r12,%rax
> > 76.82 : ffffffff81413890: lock xadd %rax,(%rbx)
> > 22.10 : ffffffff81413895: lea (%r12,%rax,1),%r15
> >
> >
> > Showing cycles for page_counter_cancel
> > Events Pcnt (>=5%)
> > Percent | Source code & Disassembly of elf for cycles (1004744 samples,
> percent: local period)
> > --------------------------------------------------------------------------------------------------
> --
> > : 160 return i + xadd(&v->counter, i);
> > 77.42 : ffffffff81413759: lock xadd %rax,(%rdi)
> > 22.34 : ffffffff8141375e: sub %rsi,%rax
> >
> >
> > Showing cycles for try_charge_memcg
> > Events Pcnt (>=5%)
> > Percent | Source code & Disassembly of elf for cycles (256531 samples,
> percent: local period)
> > --------------------------------------------------------------------------------------------------
> -
> > : 22 return __READ_ONCE((v)->counter);
> > 77.53 : ffffffff8141df86: mov 0x100(%r13),%rdx
> > : 2826 READ_ONCE(memcg->memory.high);
> > 19.45 : ffffffff8141df8d: mov 0x190(%r13),%rcx
>
> This is rephrasing the info you gave earlier ?

Yep, I just want to show some details.

>
> 16.77% [kernel] [k] page_counter_try_charge
> 16.56% [kernel] [k] page_counter_cancel
> 15.65% [kernel] [k] try_charge_memcg
>
> What matters here is a call graph.

Thanks for explanation. I re-collect it.

>
> perf record -a -g sleep 5 # While the test is running perf report --no-children -
> -stdio

Here is the output with the command you paste, it's from system wide,
I only show pieces of memcached records, and it seems to be a
callee -> caller stack trace:

9.02% mc-worker [kernel.vmlinux] [k] page_counter_try_charge
|
--9.00%--page_counter_try_charge
|
--9.00%--try_charge_memcg
mem_cgroup_charge_skmem
|
--9.00%--__sk_mem_raise_allocated
__sk_mem_schedule
|
|--5.32%--tcp_try_rmem_schedule
| tcp_data_queue
| tcp_rcv_established
| tcp_v4_do_rcv
| tcp_v4_rcv
| ip_protocol_deliver_rcu
| ip_local_deliver_finish
| ip_local_deliver
| ip_rcv
| __netif_receive_skb_one_core
| __netif_receive_skb
| process_backlog
| __napi_poll
| net_rx_action
| __do_softirq
| |
| --5.32%--do_softirq.part.0
| __local_bh_enable_ip
| __dev_queue_xmit
| ip_finish_output2
| __ip_finish_output
| ip_finish_output
| ip_output
| ip_local_out
| __ip_queue_xmit
| ip_queue_xmit
| __tcp_transmit_skb
| tcp_write_xmit
| __tcp_push_pending_frames
| tcp_push
| tcp_sendmsg_locked
| tcp_sendmsg
| inet_sendmsg
| sock_sendmsg
| ____sys_sendmsg

8.98% mc-worker [kernel.vmlinux] [k] page_counter_cancel
|
--8.97%--page_counter_cancel
|
--8.97%--page_counter_uncharge
drain_stock
__refill_stock
refill_stock
|
--8.91%--try_charge_memcg
mem_cgroup_charge_skmem
|
--8.91%--__sk_mem_raise_allocated
__sk_mem_schedule
|
|--5.41%--tcp_try_rmem_schedule
| tcp_data_queue
| tcp_rcv_established
| tcp_v4_do_rcv
| tcp_v4_rcv
| ip_protocol_deliver_rcu
| ip_local_deliver_finish
| ip_local_deliver
| ip_rcv
| __netif_receive_skb_one_core
| __netif_receive_skb
| process_backlog
| __napi_poll
| net_rx_action
| __do_softirq
| do_softirq.part.0
| __local_bh_enable_ip
| __dev_queue_xmit
| ip_finish_output2
| __ip_finish_output
| ip_finish_output
| ip_output
| ip_local_out
| __ip_queue_xmit
| ip_queue_xmit
| __tcp_transmit_skb
| tcp_write_xmit
| __tcp_push_pending_frames
| tcp_push
| tcp_sendmsg_locked
| tcp_sendmsg
| inet_sendmsg

8.78% mc-worker [kernel.vmlinux] [k] try_charge_memcg
|
--8.77%--try_charge_memcg
|
--8.76%--mem_cgroup_charge_skmem
|
--8.76%--__sk_mem_raise_allocated
__sk_mem_schedule
|
|--5.21%--tcp_try_rmem_schedule
| tcp_data_queue
| tcp_rcv_established
| tcp_v4_do_rcv
| |
| --5.21%--tcp_v4_rcv
| ip_protocol_deliver_rcu
| ip_local_deliver_finish
| ip_local_deliver
| ip_rcv
| __netif_receive_skb_one_core
| __netif_receive_skb
| process_backlog
| __napi_poll
| net_rx_action
| __do_softirq
| |
| --5.21%--do_softirq.part.0
| __local_bh_enable_ip
| __dev_queue_xmit
| ip_finish_output2
| __ip_finish_output
| ip_finish_output
| ip_output
| ip_local_out
| __ip_queue_xmit
| ip_queue_xmit
| __tcp_transmit_skb
| tcp_write_xmit
| __tcp_push_pending_frames
| tcp_push
| tcp_sendmsg_locked
| tcp_sendmsg
| inet_sendmsg
| sock_sendmsg
| ____sys_sendmsg
| ___sys_sendmsg
| __sys_sendmsg

>
> What precise kernel are you using btw ?

The above data is collected with 'net-next/main' git branch:
base-commit: ed23734c23d2 ("Merge tag 'net-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")