From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: RFC: NAPI packet weighting patch Date: 21 Jun 2005 23:47:07 +0200 Message-ID: References: <468F3FDA28AA87429AD807992E22D07E0450C00B@orsmsx408> <42A5284C.3060808@osdl.org> <20050621.132044.115910664.davem@davemloft.net> <42B87ACF.3080800@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@oss.sgi.com, davem@redhat.com Return-path: To: Rick Jones In-Reply-To: <42B87ACF.3080800@hp.com> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Rick Jones writes: > > Actually, it has a _HUGE_ _HUGE_ impact. If you pass the big buffer > > up, the receiving socket gets charged for the size of the huge buffer, > > not for just the size of the packet contained within. This makes > > sockets get overcharged for data reception, and it can cause all kinds > > of performance problems. > > Then copy when the socket is about to fill with overhead bytes? The stack has supported that since 2.4. Mostly because it is the only sane way to handle devices with very big MTU. But it turns off all kinds of fast paths before it happens, I guess that is what David was refering too. However I suspect the cut-off points with rx-copybreak in common driver have been often tuned before that code was introduced and it might be worth to do some retesting. -Andi