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Date: Wed, 12 Nov 2008 21:11:34 +0300 From: Evgeniy Polyakov <zbr@...emap.net> To: "Lovich, Vitali" <vlovich@...lcomm.com> Cc: Johann Baudy <johaahn@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: [PATCH] Packet socket: mmapped IO: PACKET_TX_RING On Wed, Nov 12, 2008 at 09:59:20AM -0800, Lovich, Vitali (vlovich@...lcomm.com) wrote: > They aren't racy - not in the sense that your suggestion would make it. With current splice & sendfile, when it returns from the syscall, the user knows that it has been transmitted and thus can continue using the file descriptors & memory (in the case of vmsplice). However, with your suggestion, the user could actually never know when it's safe to write into memory (even in a single-threaded situation). Thus it is racy in a single-threaded situation (even on a UP it's potentially racy) which is a pretty amazing feat. Consider: Problem is, that when sendfile() returns nothing has been transferred. And in some NICs it will take a while to actually make a transfer. And what you wrote below is exactly the same problem as exists with splice/sendfile in particular and ->sendpage() in general. Please also update your mailer to wrap strings into 80-or-so lines, it is hard to answer into the middle of the paragraph. -- Evgeniy Polyakov -- 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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