From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [STRAW MAN PATCH] sch_teql doesn't load-balance ppp(oatm) slaves Date: Tue, 27 Mar 2012 21:35:22 +0100 Message-ID: <1332880522.2058.67.camel@shinybook.infradead.org> References: <1332450218.32446.79.camel@shinybook.infradead.org> <20120322.230331.1623101647193498167.davem@davemloft.net> <1332672230.32446.160.camel@shinybook.infradead.org> <20120325.173635.1909319488008466320.davem@davemloft.net> <1332875447.2058.48.camel@shinybook.infradead.org> <1332878138.3547.41.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-0pE+uX0XWdU8xvHvBBRs" Cc: David Miller , paulus@samba.org, netdev@vger.kernel.org To: Eric Dumazet Return-path: Received: from casper.infradead.org ([85.118.1.10]:57204 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753260Ab2C0Uf2 (ORCPT ); Tue, 27 Mar 2012 16:35:28 -0400 In-Reply-To: <1332878138.3547.41.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: --=-0pE+uX0XWdU8xvHvBBRs Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2012-03-27 at 21:55 +0200, Eric Dumazet wrote: > I have no idea why you added all these barriers...=20 Um, some of them snuck in while I was working it out, and then I couldn't prove to myself that they *weren't* needed, so I left them. We definitely need a write barrier in pppoatm_pop() after the change to sk->sk_sndbuf (which happens in the old_pop routine) and the increment of pvcc->inflight. Those changes must hit *before* the test/change of the BLOCKED bit. But there's an implicit barrier in test_and_clear_bit() which should achieve that, so the specific barrier you highlight may well be superfluous. I could have sworn I had a reason for it at the time, but can't justify it now. On the pppoatm_may_send() side, the change to the BLOCKED bit needs a corresponding read barrier after it, to ensure that its subsequent checks of sk->sndbuf and pvcc->inflight are looking at the data which were written before the BLOCKED bit is tested in pppoatm_pop(). But I suppose we can probably dispense with the barrier *before* setting the BLOCKED bit in pppoatm_may_send(), and the barriers after increasing pvcc->inflight. If it looks sane other than that, I can knock up a new patch with a S-O-B. Thanks for reviewing... --=20 dwmw2 --=-0pE+uX0XWdU8xvHvBBRs Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIITvzCCBi0w ggQVoAMCAQICAwCtOTANBgkqhkiG9w0BAQUFADBUMRQwEgYDVQQKEwtDQWNlcnQgSW5jLjEeMBwG A1UECxMVaHR0cDovL3d3dy5DQWNlcnQub3JnMRwwGgYDVQQDExNDQWNlcnQgQ2xhc3MgMyBSb290 MB4XDTEwMDYxMjEwMDMwMFoXDTEyMDYxMTEwMDMwMFowgegxGDAWBgNVBAMTD0RhdmlkIFdvb2Ro b3VzZTEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzEfMB0GCSqGSIb3DQEJARYQ ZGF2aWRAd29vZGhvdS5zZTEoMCYGCSqGSIb3DQEJARYZZGF2aWQud29vZGhvdXNlQGludGVsLmNv bTEkMCIGCSqGSIb3DQEJARYVZHdtdzJAbGludXguaW50ZWwuY29tMTcwNQYJKoZIhvcNAQkBFigx MDg3MmEwN2Y2ZDdlMWUwN2Y1NWZmMTcyYTAzYjMwMGVlYWFkMjAzMIIBIjANBgkqhkiG9w0BAQEF AAOCAQ8AMIIBCgKCAQEA29OPhNvMxBMW83psWdVhZDtmJvgN+tBEp1r6MZamONsR0k81a6fDFwJz M0fEzEbV/bDG102QyX/xXC/0IpKV4acnqESC+sTHUmRwxfRKGNmR6t2iwEs2Y5kQDF31JxbCt49w 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