From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D9D59C433B4 for ; Fri, 9 Apr 2021 05:31:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B344361179 for ; Fri, 9 Apr 2021 05:31:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233225AbhDIFbX (ORCPT ); Fri, 9 Apr 2021 01:31:23 -0400 Received: from mx2.suse.de ([195.135.220.15]:44124 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229715AbhDIFbU (ORCPT ); Fri, 9 Apr 2021 01:31:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617946267; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dUyZP7P4xA+xPzX2ba0l8kT9zCH9NJ6E9eFzEIksaXQ=; b=QlH7AvwABeg+r4h+GIi/sUzv+gfX5X1Ye35qtMKCLXqeNhnf4kMPyCap2FTjWVdnVX50Nz SxpRHir+TKZjOill5k2vhP9mUm60SSNoUTwyFhr/X69sKYL/V7ayyiG9gWbs1S5FK41Br6 /JJX5+Ej++b148S8PdcfYqHEf7xE90Q= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E7376B01C; Fri, 9 Apr 2021 05:31:06 +0000 (UTC) To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org Cc: olteanv@gmail.com, ast@kernel.org, daniel@iogearbox.net, andriin@fb.com, edumazet@google.com, weiwan@google.com, cong.wang@bytedance.com, ap420073@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@openeuler.org, mkl@pengutronix.de, linux-can@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, bpf@vger.kernel.org, jonas.bonn@netrounds.com, pabeni@redhat.com, mzhivich@akamai.com, johunt@akamai.com, albcamus@gmail.com, kehuan.feng@gmail.com, a.fatoum@pengutronix.de, atenart@kernel.org, alexander.duyck@gmail.com, Jiri Kosina References: <1616641991-14847-1-git-send-email-linyunsheng@huawei.com> From: Juergen Gross Subject: Re: [PATCH net v3] net: sched: fix packet stuck problem for lockless qdisc Message-ID: Date: Fri, 9 Apr 2021 07:31:03 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <1616641991-14847-1-git-send-email-linyunsheng@huawei.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="KNfSBDESab9zDoXGXKJSsQrdHG9FC4fMd" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --KNfSBDESab9zDoXGXKJSsQrdHG9FC4fMd Content-Type: multipart/mixed; boundary="LSz7PCDIMfnx6xL5FBKNaZUVKlHLEdp1Z"; protected-headers="v1" From: Juergen Gross To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org Cc: olteanv@gmail.com, ast@kernel.org, daniel@iogearbox.net, andriin@fb.com, edumazet@google.com, weiwan@google.com, cong.wang@bytedance.com, ap420073@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@openeuler.org, mkl@pengutronix.de, linux-can@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, bpf@vger.kernel.org, jonas.bonn@netrounds.com, pabeni@redhat.com, mzhivich@akamai.com, johunt@akamai.com, albcamus@gmail.com, kehuan.feng@gmail.com, a.fatoum@pengutronix.de, atenart@kernel.org, alexander.duyck@gmail.com, Jiri Kosina Message-ID: Subject: Re: [PATCH net v3] net: sched: fix packet stuck problem for lockless qdisc References: <1616641991-14847-1-git-send-email-linyunsheng@huawei.com> In-Reply-To: <1616641991-14847-1-git-send-email-linyunsheng@huawei.com> --LSz7PCDIMfnx6xL5FBKNaZUVKlHLEdp1Z Content-Type: multipart/mixed; boundary="------------CDB4D2BA5B7A94706A1D1B2A" Content-Language: en-US This is a multi-part message in MIME format. --------------CDB4D2BA5B7A94706A1D1B2A Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 25.03.21 04:13, Yunsheng Lin wrote: > Lockless qdisc has below concurrent problem: > cpu0 cpu1 > . . > q->enqueue . > . . > qdisc_run_begin() . > . . > dequeue_skb() . > . . > sch_direct_xmit() . > . . > . q->enqueue > . qdisc_run_begin() > . return and do nothing > . . > qdisc_run_end() . >=20 > cpu1 enqueue a skb without calling __qdisc_run() because cpu0 > has not released the lock yet and spin_trylock() return false > for cpu1 in qdisc_run_begin(), and cpu0 do not see the skb > enqueued by cpu1 when calling dequeue_skb() because cpu1 may > enqueue the skb after cpu0 calling dequeue_skb() and before > cpu0 calling qdisc_run_end(). >=20 > Lockless qdisc has below another concurrent problem when > tx_action is involved: >=20 > cpu0(serving tx_action) cpu1 cpu2 > . . . > . q->enqueue . > . qdisc_run_begin() . > . dequeue_skb() . > . . q->enqueue > . . . > . sch_direct_xmit() . > . . qdisc_run_begin() > . . return and do nothing > . . . > clear __QDISC_STATE_SCHED . . > qdisc_run_begin() . . > return and do nothing . . > . . . > . qdisc_run_end() . >=20 > This patch fixes the above data race by: > 1. Get the flag before doing spin_trylock(). > 2. If the first spin_trylock() return false and the flag is not > set before the first spin_trylock(), Set the flag and retry > another spin_trylock() in case other CPU may not see the new > flag after it releases the lock. > 3. reschedule if the flags is set after the lock is released > at the end of qdisc_run_end(). >=20 > For tx_action case, the flags is also set when cpu1 is at the > end if qdisc_run_end(), so tx_action will be rescheduled > again to dequeue the skb enqueued by cpu2. >=20 > Only clear the flag before retrying a dequeuing when dequeuing > returns NULL in order to reduce the overhead of the above double > spin_trylock() and __netif_schedule() calling. >=20 > The performance impact of this patch, tested using pktgen and > dummy netdev with pfifo_fast qdisc attached: >=20 > threads without+this_patch with+this_patch delta > 1 2.61Mpps 2.60Mpps -0.3% > 2 3.97Mpps 3.82Mpps -3.7% > 4 5.62Mpps 5.59Mpps -0.5% > 8 2.78Mpps 2.77Mpps -0.3% > 16 2.22Mpps 2.22Mpps -0.0% >=20 > Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking") > Signed-off-by: Yunsheng Lin I have a setup which is able to reproduce the issue quite reliably: In a Xen guest I'm mounting 8 NFS shares and run sysbench fileio on each of them. The average latency reported by sysbench is well below 1 msec, but at least once per hour I get latencies in the minute range. With this patch I don't see these high latencies any longer (test is running for more than 20 hours now). So you can add my: Tested-by: Juergen Gross Juergen --------------CDB4D2BA5B7A94706A1D1B2A Content-Type: application/pgp-keys; name="OpenPGP_0xB0DE9DD628BF132F.asc" Content-Transfer-Encoding: quoted-printable Content-Disposition: attachment; filename="OpenPGP_0xB0DE9DD628BF132F.asc" -----BEGIN PGP PUBLIC KEY BLOCK----- xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOBy= cWx w3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJvedYm8O= f8Z d621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJNwQpd369y= 9bf IhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvxXP3FAp2pkW0xq= G7/ 377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEBAAHNHEp1ZXJnZW4gR= 3Jv c3MgPGpnQHBmdXBmLm5ldD7CwHkEEwECACMFAlOMcBYCGwMHCwkIBwMCAQYVCAIJCgsEFgIDA= QIe AQIXgAAKCRCw3p3WKL8TL0KdB/93FcIZ3GCNwFU0u3EjNbNjmXBKDY4FUGNQH2lvWAUy+dnyT= hpw dtF/jQ6j9RwE8VP0+NXcYpGJDWlNb9/JmYqLiX2Q3TyevpB0CA3dbBQp0OW0fgCetToGIQrg0= MbD 1C/sEOv8Mr4NAfbauXjZlvTj30H2jO0u+6WGM6nHwbh2l5O8ZiHkH32iaSTfN7Eu5RnNVUJbv= oPH Z8SlM4KWm8rG+lIkGurqqu5gu8q8ZMKdsdGC4bBxdQKDKHEFExLJK/nRPFmAuGlId1E3fe10v= 5QL +qHI3EIPtyfE7i9Hz6rVwi7lWKgh7pe0ZvatAudZ+JNIlBKptb64FaiIOAWDCx1SzR9KdWVyZ= 2Vu IEdyb3NzIDxqZ3Jvc3NAc3VzZS5jb20+wsB5BBMBAgAjBQJTjHCvAhsDBwsJCAcDAgEGFQgCC= QoL BBYCAwECHgECF4AACgkQsN6d1ii/Ey/HmQf/RtI7kv5A2PS4RF7HoZhPVPogNVbC4YA6lW7Dr= Wf0 teC0RR3MzXfy6pJ+7KLgkqMlrAbN/8Dvjoz78X+5vhH/rDLa9BuZQlhFmvcGtCF8eR0T1v0nC= /nu AFVGy+67q2DH8As3KPu0344TBDpAvr2uYM4tSqxK4DURx5INz4ZZ0WNFHcqsfvlGJALDeE0Lh= ITT d9jLzdDad1pQSToCnLl6SBJZjDOX9QQcyUigZFtCXFst4dlsvddrxyqT1f17+2cFSdu7+ynLm= XBK 7abQ3rwJY8SbRO2iRulogc5vr/RLMMlscDAiDkaFQWLoqHHOdfO9rURssHNN8WkMnQfvUewRz= 80h SnVlcmdlbiBHcm9zcyA8amdyb3NzQG5vdmVsbC5jb20+wsB5BBMBAgAjBQJTjHDXAhsDBwsJC= AcD AgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey8PUQf/ehmgCI9jB9hlgexLvgOtf7PJn= FOX gMLdBQgBlVPO3/D9R8LtF9DBAFPNhlrsfIG/SqICoRCqUcJ96Pn3P7UUinFG/I0ECGF4EvTE1= jnD kfJZr6jrbjgyoZHiw/4BNwSTL9rWASyLgqlA8u1mf+c2yUwcGhgkRAd1gOwungxcwzwqgljf0= N51 N5JfVRHRtyfwq/ge+YEkDGcTU6Y0sPOuj4Dyfm8fJzdfHNQsWq3PnczLVELStJNdapwPOoE+l= otu fe3AM2vAEYJ9rTz3Cki4JFUsgLkHFqGZarrPGi1eyQcXeluldO3m91NK/1xMI3/+8jbO0tsn1= tqS EUGIJi7ox80eSnVlcmdlbiBHcm9zcyA8amdyb3NzQHN1c2UuZGU+wsB5BBMBAgAjBQJTjHDrA= hsD BwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey+LhQf9GL45eU5vOowA2u5N3= g3O ZUEBmDHVVbqMtzwlmNC4k9Kx39r5s2vcFl4tXqW7g9/ViXYuiDXb0RfUpZiIUW89siKrkzmQ5= dM7 wRqzgJpJwK8Bn2MIxAKArekWpiCKvBOB/Cc+3EXE78XdlxLyOi/NrmSGRIov0karw2RzMNOu5= D+j LRZQd1Sv27AR+IP3I8U4aqnhLpwhK7MEy9oCILlgZ1QZe49kpcumcZKORmzBTNh30FVKK1Evm= V2x AKDoaEOgQB4iFQLhJCdP1I5aSgM5IVFdn7v5YgEYuJYx37IoN1EblHI//x/e2AaIHpzK5h88N= Eaw QsaNRpNSrcfbFmAg987ATQRTjHAWAQgAyzH6AOODMBjgfWE9VeCgsrwH3exNAU32gLq2xvjpW= nHI s98ndPUDpnoxWQugJ6MpMncr0xSwFmHEgnSEjK/PAjppgmyc57BwKII3sV4on+gDVFJR6Y8ZR= wgn BC5mVM6JjQ5xDk8WRXljExRfUX9pNhdE5eBOZJrDRoLUmmjDtKzWaDhIg/+1Hzz93X4fCQkNV= bVF LELU9bMaLPBG/x5q4iYZ2k2ex6d47YE1ZFdMm6YBYMOljGkZKwYde5ldM9mo45mmwe0icXKLk= pEd IXKTZeKDO+Hdv1aqFuAcccTg9RXDQjmwhC3yEmrmcfl0+rPghO0Iv3OOImwTEe4co3c1mwARA= QAB wsBfBBgBAgAJBQJTjHAWAhsMAAoJELDendYovxMvQ/gH/1ha96vm4P/L+bQpJwrZ/dneZcmEw= Tbe 8YFsw2V/Buv6Z4Mysln3nQK5ZadD534CF7TDVft7fC4tU4PONxF5D+/tvgkPfDAfF77zy2AH1= vJz Q1fOU8lYFpZXTXIHb+559UqvIB8AdgR3SAJGHHt4RKA0F7f5ipYBBrC6cyXJyyoprT10EMvU8= VGi wXvTyJz3fjoYsdFzpWPlJEBRMedCot60g5dmbdrZ5DWClAr0yau47zpWj3enf1tLWaqcsuylW= svi uGjKGw7KHQd3bxALOknAp4dN3QwBYCKuZ7AddY9yjynVaD5X7nF9nO5BjR/i1DG86lem3iBDX= zXs ZDn8R38=3D =3D2wuH -----END PGP PUBLIC KEY BLOCK----- --------------CDB4D2BA5B7A94706A1D1B2A-- --LSz7PCDIMfnx6xL5FBKNaZUVKlHLEdp1Z-- --KNfSBDESab9zDoXGXKJSsQrdHG9FC4fMd Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmBv5pcFAwAAAAAACgkQsN6d1ii/Ey+U WQf/dvUZrKhZVIiZyvAc888M6ZYmJE5fOb/Cm0XkTJe0TiBSy6Q3HejzXgO+yFIWWKlb8VJ2s48N Ei0XoRMl9wi1ORkrAc/NBi6GqvPRVP0rdCgZ8JbjyP11XSWSrii/H+VAgxLHckSmizh9Inf5SvLl eWwcQ/cCOLicSNSEkbUAq+VVontel2FA9M4sVeSOyjkb9f3+Y8E8BkfPsTtuugTjtebQL4p3kFjz fBCIdP9CFVzHbRTw6XH9Xp9mRv5TDcNyp811nVFy9kgYv9oAbJXzd1WCbMSCrIGLC4drvUxoYswq RnSTgsBV72NTulgyo4T19cwWD1HDYS+D+R7mLLCr9w== =Pnqx -----END PGP SIGNATURE----- --KNfSBDESab9zDoXGXKJSsQrdHG9FC4fMd--