Date: Sat, 13 Oct 2012 12:24:21 -0700 From: Jack Vogel <jfvogel@gmail.com> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: "Alexander V. Chernikov" <melifaro@freebsd.org>, net@freebsd.org Subject: Re: ixgbe & if_igb RX ring locking Message-ID: <CAFOYbc=N87_OECto7B8jdzmRZA-yoa_JWgvVc8kwpK9umO97rQ@mail.gmail.com> In-Reply-To: <20121013182223.GA73341@onelab2.iet.unipi.it> References: <5079A9A1.4070403@FreeBSD.org> <20121013182223.GA73341@onelab2.iet.unipi.it>
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On Sat, Oct 13, 2012 at 11:22 AM, Luigi Rizzo <rizzo@iet.unipi.it> wrote:
> On Sat, Oct 13, 2012 at 09:49:21PM +0400, Alexander V. Chernikov wrote:
> > Hello list!
> >
> >
> > Packets receiving code for both ixgbe and if_igb looks like the
> following:
> >
> >
> > ixgbe_msix_que
> >
> > -- ixgbe_rxeof()
> > {
> > IXGBE_RX_LOCK(rxr);
> > while
> > {
> > get_packet;
> >
> > -- ixgbe_rx_input()
> > {
> > ++ IXGBE_RX_UNLOCK(rxr);
> > if_input(packet);
> > ++ IXGBE_RX_LOCK(rxr);
> > }
> >
> > }
> > IXGBE_RX_UNLOCK(rxr);
> > }
> >
> > Lines marked with ++ appeared in r209068(igb) and r217593(ixgbe).
> >
> > These lines probably do LORs masking (if any) well.
> > However, such change introduce quite significant performance drop:
> >
> > On my routing setup (nearly the same from previous -Intel 10G thread in
> > -net) adding lock/unlock causes 2.8MPPS decrease to 2.3MPPS which is
> > nearly 20%.
>
> one option could be (same as it is done in the timer
> routine in dummynet) to build a list of all the packets
> that need to be sent to if_input(), and then call
> if_input with the entire list outside the lock.
>
> It would be even easier if we modify the various *_input()
> routines to handle a list of mbufs instead of just one.
>
> cheers
> luigi
>
> Very interesting idea Luigi, will have to get that some thought.
Jack
> So my questions are:
> >
> > Can any real LORs happen in some complex setup? (I can't imagine any).
> > If so: maybe we can somehow avoid/workaround such cases? (and consider
> > removing those locks).
> >
> >
> >
> > --
> > WBR, Alexander
> >
> > _______________________________________________
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>
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