Hi Eric,
On Fri, Jun 14, 2019 at 04:22:20PM -0700, Eric Dumazet wrote:
> Feng Tang reported a performance regression after introduction
> of per TCP socket tx/rx caches, for TCP over loopback (netperf)
>
> There is high chance the regression is caused by a change on
> how well the 32 KB per-thread page (current->task_frag) can
> be recycled, and lack of pcp caches for order-3 pages.
Exactly! When I checked the regression, I did several experiments,
and thought of the simliar idea to add the per-CPU orderX pcp list,
the other idea is to add a order3 list in per-cpu softnet_data as
local cache.
Thanks,
Feng
>
> I could not reproduce the regression myself, cpus all being
> spinning on the mm spinlocks for page allocs/freeing, regardless
> of enabling or disabling the per tcp socket caches.
>
> It seems best to disable the feature by default, and let
> admins enabling it.
>
> MM layer either needs to provide scalable order-3 pages
> allocations, or could attempt a trylock on zone->lock if
> the caller only attempts to get a high-order page and is
> able to fallback to order-0 ones in case of pressure.
>
> Tests run on a 56 cores host (112 hyper threads)
>
> - 35.49% netperf [kernel.vmlinux] [k]
> queued_spin_lock_slowpath
> - 35.49% queued_spin_lock_slowpath
> - 18.18% get_page_from_freelist
> - __alloc_pages_nodemask
> - 18.18% alloc_pages_current
> skb_page_frag_refill
> sk_page_frag_refill
> tcp_sendmsg_locked
> tcp_sendmsg
> inet_sendmsg
> sock_sendmsg
> __sys_sendto
> __x64_sys_sendto
> do_syscall_64
> entry_SYSCALL_64_after_hwframe
> __libc_send
> + 17.31% __free_pages_ok
> + 31.43% swapper [kernel.vmlinux] [k] intel_idle
> + 9.12% netperf [kernel.vmlinux] [k]
> copy_user_enhanced_fast_string
> + 6.53% netserver [kernel.vmlinux] [k]
> copy_user_enhanced_fast_string
> + 0.69% netserver [kernel.vmlinux] [k]
> queued_spin_lock_slowpath
> + 0.68% netperf [kernel.vmlinux] [k]
> skb_release_data
> + 0.52% netperf [kernel.vmlinux] [k]
> tcp_sendmsg_locked
> 0.46% netperf [kernel.vmlinux] [k]
> _raw_spin_lock_irqsave
>
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Reported-by: Feng Tang <feng.t...@intel.com>
> ---
> include/net/sock.h | 4 +++-
> net/ipv4/sysctl_net_ipv4.c | 8 ++++++++
> 2 files changed, 11 insertions(+), 1 deletion(-)
