linux-kernel - Re: [-next] Regression: ssh log in slowdown

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Date:	Fri, 13 Jun 2014 10:43:47 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Tom Herbert <therbert@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux-Next <linux-next@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [-next] Regression: ssh log in slowdown

Hi Tom,

On Fri, Jun 13, 2014 at 10:21 AM, Tom Herbert <therbert@...gle.com> wrote:
>> I assume this is the series "[PATCH 0/4] Checksum fixes"
>> (marc.info/?l=linux-netdev&m=140261417832399&w=2)?
>>
> Yes.
>
>> As I'm not subscribed to netdev, I cannot reply to that thread.
>>
>> "[PATCH 1/4] net: Fix save software checksum complete" fixes the issue
>> for me.
>> However, "[PATCH 2/4] udp: call __skb_checksum_complete when doing full
>> checksum" reintroduces the exact same bad behavior :-(
>>
> This implies the problem is happening in UDP path. AFAICT skb->csum is
> correct, and I don't seem to be able to reproduce the issue on my setup.
> It is possible that an skb copy is happening in which case we don't copy
> csum_valid so that checksum_unnecessary would fail in this case.
>
> Can you try with the patch below. Thanks!
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index bf92824..9cd5344 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -689,6 +689,9 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
>         new->ooo_okay           = old->ooo_okay;
>         new->no_fcs             = old->no_fcs;
>         new->encapsulation      = old->encapsulation;
> +       new->encap_hdr_csum     = old->encap_hdr_csum;
> +       new->csum_valid         = old->csum_valid;
> +       new->csum_complete_sw   = old->csum_complete_sw;
>  #ifdef CONFIG_XFRM
>         new->sp                 = secpath_get(old->sp);
>  #endif

Thanks, I applied the series "[PATCH 0/4] Checksum fixes", and the fix
above, but it doesn't help.

Note that I'm also using NFS root, which doesn't seem to be affected.
I can happily run "ls -R /" on the serial console during the 10 s delay in ssh.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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