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Date: Fri, 04 Jun 2010 06:05:54 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Sonic Zhang <sonic.adi@...il.com> Cc: David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>, uclinux-dist-devel <uclinux-dist-devel@...ckfin.uclinux.org> Subject: Re: [PATCH v2] netdev:bfin_mac: reclaim and free tx skb as soon as possible after transfer Le vendredi 04 juin 2010 à 11:29 +0800, Sonic Zhang a écrit : > David, > > Any comments? > > Thanks > > Sonic > > On Thu, Jun 3, 2010 at 11:48 AM, sonic zhang <sonic.adi@...il.com> wrote: > > >From 40560ae9e8db42e2d2259b791ace160534c9a0f2 Mon Sep 17 00:00:00 2001 > > From: Sonic Zhang <sonic.zhang@...log.com> > > Date: Thu, 3 Jun 2010 11:44:33 +0800 > > Subject: [PATCH v2] netdev:bfin_mac: reclaim and free tx skb as soon as possible after transfer > > > > SKBs hold onto resources that can't be held indefinitely, such as TCP > > socket references and netfilter conntrack state. So if a packet is left > > in TX ring for a long time, there might be a TCP socket that cannot be > > closed and freed up. > > > > Current blackfin EMAC driver always reclaim and free used tx skbs in future > > transfers. The problem is that future transfer may not come as soon as > > possible. This patch start a timer after transfer to reclaim and free skb. > > There is nearly no performance drop with this patch. > > > > TX interrupt is not enabled for 2 reasons: > > > > 1) If Blackfin EMAC TX transfer control is turned on, endless TX > > interrupts are triggered no matter if TX DMA is enabled. Since DMA walks > > down the ring automatically, TX transfer control can't be turned off in the > > middle. The only way is to disable TX interrupt completely. > > > > 2) skb can not be freed from interrupt context. A work queue or tasklet > > has to be created, which introduce more overhead than timer only solution. > > Could you elaborate on this second point ? skb can be freed from interrupt context using appropriate API : 1) If from NAPI context, no special care is needed and use dev_kfree_skb(). 2) If from hard irq context, use dev_kfree_skb_irq() : With recent changes, skb is probably already orphaned and can be freed immediately. In the unlikely case it is not yet orphaned, skb is queued in softnet_data.completion_queue. -- 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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