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Date: Fri, 21 Sep 2012 11:00:57 +0200 From: Joakim Tjernlund <joakim.tjernlund@...nsmode.se> To: David Miller <davem@...emloft.net> Cc: netdev@...r.kernel.org, romieu@...zoreil.com Subject: Re: [PATCH v2] ucc_geth: Reduce IRQ off in xmit path David Miller <davem@...emloft.net> wrote on 2012/09/20 23:08:52: > > From: Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se> > Date: Thu, 20 Sep 2012 10:17:01 +0200 > > > Currently ucc_geth_start_xmit wraps IRQ off for the > > whole body just to be safe. > > Reduce the IRQ off period to a minimum. > > > > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se> > > --- > > > > v2: Move assignment of ugeth->tx_skbuff[txQ][ugeth->skb_curtx[txQ]] > > inside IRQ off section to prevent racing against > > ucc_geth_tx(). Spotted by Francois Romieu <romieu@...zoreil.com> > > I agree with Francois's initial analysis, and disagree with you're > response to him, wrt. the suggest to remove all locking entirely. > > Unlike what you claim, there isn't much of a gain at all from merely > make the window of lock holding smaller, especially on the scale > in which you are doing it here. > > Whereas removing the lock and the atomic completely, as tg3 does, > will give very significant performance gains. > > The locking cost of grabbing the spinlock, and the memory transactions > associated with it, dominate. > > Furthermore, even if the gains of your change are non-trivial, you > haven't documented it. So unless you should some noticable gains from > this, it's just code masterbation as far as I'm concerned and I'm > therefore inclined to not apply patches like this. > > TG3's core interrupt locking is not that difficult to understand and > replicate in other drivers, so I dismiss your attempts to avoid that > approach on difficulty grounds as well. OK, I will give it a go. Got something working that I will send in shortly. I hope the other patches were OK? Jocke -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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