lkml.org 
[lkml]   [2013]   [Oct]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86: Run checksumming in parallel accross multiple alu's
On Mon, Oct 14, 2013 at 02:07:48PM -0700, Eric Dumazet wrote:
> On Mon, 2013-10-14 at 09:49 +0200, Ingo Molnar wrote:
> > * Andi Kleen <andi@firstfloor.org> wrote:
> >
> > > Neil Horman <nhorman@tuxdriver.com> writes:
> > >
> > > > Sébastien Dugué reported to me that devices implementing ipoib (which
> > > > don't have checksum offload hardware were spending a significant
> > > > amount of time computing
> > >
> > > Must be an odd workload, most TCP/UDP workloads do copy-checksum
> > > anyways. I would rather investigate why that doesn't work.
> >
> > There's a fair amount of csum_partial()-only workloads, a packet does not
> > need to hit user-space to be a significant portion of the system's
> > workload.
> >
> > That said, it would indeed be nice to hear which particular code path was
> > hit in this case, if nothing else then for education purposes.
>
> Many NIC do not provide a CHECKSUM_COMPLETE information for encapsulated
> frames, meaning we have to fallback to software csum to validate
> TCP frames, once tunnel header is pulled.
>
> So to reproduce the issue, all you need is to setup a GRE tunnel between
> two hosts, and use any tcp stream workload.
>
> Then receiver profile looks like :
>
> 11.45% [kernel] [k] csum_partial
> 3.08% [kernel] [k] _raw_spin_lock
> 3.04% [kernel] [k] intel_idle
> 2.73% [kernel] [k] ipt_do_table
> 2.57% [kernel] [k] __netif_receive_skb_core
> 2.15% [kernel] [k] copy_user_generic_string
> 2.05% [kernel] [k] __hrtimer_start_range_ns
> 1.42% [kernel] [k] ip_rcv
> 1.39% [kernel] [k] kmem_cache_free
> 1.36% [kernel] [k] _raw_spin_unlock_irqrestore
> 1.24% [kernel] [k] __schedule
> 1.13% [bnx2x] [k] bnx2x_rx_int
> 1.12% [bnx2x] [k] bnx2x_start_xmit
> 1.11% [kernel] [k] fib_table_lookup
> 0.99% [ip_tunnel] [k] ip_tunnel_lookup
> 0.91% [ip_tunnel] [k] ip_tunnel_rcv
> 0.90% [kernel] [k] check_leaf.isra.7
> 0.89% [kernel] [k] nf_iterate
>
As I noted previously the workload that this got reported on was ipoib, which
has a simmilar profile, since infiniband cards tend to not be able to do
checksum offload for ip frames.

Neil

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2013-10-15 15:41    [W:0.140 / U:0.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site