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(Authenticated sender: mkl@blackshift.org) by smtp.blackshift.org (Postfix) with ESMTPSA id 559F75F5AAB; Mon, 15 Mar 2021 13:09:36 +0000 (UTC) To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org, olteanv@gmail.com Cc: 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, linux-can@vger.kernel.org References: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> From: Marc Kleine-Budde Autocrypt: addr=mkl@pengutronix.de; prefer-encrypt=mutual; keydata= mQINBFFVq30BEACtnSvtXHoeHJxG6nRULcvlkW6RuNwHKmrqoksispp43X8+nwqIFYgb8UaX zu8T6kZP2wEIpM9RjEL3jdBjZNCsjSS6x1qzpc2+2ivjdiJsqeaagIgvy2JWy7vUa4/PyGfx QyUeXOxdj59DvLwAx8I6hOgeHx2X/ntKAMUxwawYfPZpP3gwTNKc27dJWSomOLgp+gbmOmgc 6U5KwhAxPTEb3CsT5RicsC+uQQFumdl5I6XS+pbeXZndXwnj5t84M+HEj7RN6bUfV2WZO/AB 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0yCEJ41rW/p3UpTV9wwE2VbGD1XjzVKl8SuAUfjjcGGys3yk5XQ5cccWTCwsVdo2uAcY1MVM HhN6YJjnMqbFoHQq0H+2YenTlTBn2Wsp8TIytE1GL6EbaPWbMh3VLRcihlMj28OUWGSERxat xlygDG5cBiY3snN3xJyBroh5xk/sHRgOdHpmujnFyu77y4RTZ2W8 Subject: Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc Message-ID: <4b02d9bb-772f-ff40-b865-ea87bd1bea6e@pengutronix.de> Date: Mon, 15 Mar 2021 14:09:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="XfdkZiGWe4GpXgPyF3Eq71MC2ms5K2wwq" X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --XfdkZiGWe4GpXgPyF3Eq71MC2ms5K2wwq Content-Type: multipart/mixed; boundary="nVncz7ZIHzuqTZClRZDr3c4OVwDWj5Ycp"; protected-headers="v1" From: Marc Kleine-Budde To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org, olteanv@gmail.com Cc: 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, linux-can@vger.kernel.org Message-ID: <4b02d9bb-772f-ff40-b865-ea87bd1bea6e@pengutronix.de> Subject: Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc References: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> In-Reply-To: <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> --nVncz7ZIHzuqTZClRZDr3c4OVwDWj5Ycp Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: quoted-printable On 3/15/21 4:10 AM, Yunsheng Lin wrote: > Currently pfifo_fast has both TCQ_F_CAN_BYPASS and TCQ_F_NOLOCK > flag set, but queue discipline by-pass does not work for lockless > qdisc because skb is always enqueued to qdisc even when the qdisc > is empty, see __dev_xmit_skb(). >=20 > This patch calls sch_direct_xmit() to transmit the skb directly > to the driver for empty lockless qdisc too, which aviod enqueuing > and dequeuing operation. qdisc->empty is set to false whenever a > skb is enqueued, see pfifo_fast_enqueue(), and is set to true when > skb dequeuing return NULL, see pfifo_fast_dequeue(), a spinlock is > added to avoid the race between enqueue/dequeue and qdisc->empty > setting. >=20 > If there is requeued skb in q->gso_skb, and qdisc->empty is true, > do not allow bypassing requeued skb. enqueuing and dequeuing in > q->gso_skb is always protected by qdisc->seqlock, so is the access > of q->gso_skb by skb_queue_empty(); >=20 > Also, qdisc is scheduled at the end of qdisc_run_end() when q->empty > is false to avoid packet stuck problem. >=20 > The performance for ip_forward test increases about 10% with this > patch. >=20 > Signed-off-by: Yunsheng Lin I gave it a short test on a single core imx. No problem here. Marc --=20 Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | --nVncz7ZIHzuqTZClRZDr3c4OVwDWj5Ycp-- --XfdkZiGWe4GpXgPyF3Eq71MC2ms5K2wwq Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEK3kIWJt9yTYMP3ehqclaivrt76kFAmBPXI0ACgkQqclaivrt 76kzZAgArkElmvsUkhVVnZlZ8tzI2BkmR+z2RwCfUGdUVPAFVdBlp/UdH9aV1gEJ 3WPLeMrXrAyOS+MSh4u1USIM3YJ7DQhBlZaxORx5uY2YUqu5Ejftbk1DjhKLc7fj yM0QzHx37e4soGNMYoKeX4NCIC71CE7YspUmpiav09ZkWBU0eoGOLYtfBQZ/WTYF MzUbrPH2bi0F3c8mCFr2AQ5KTFkc8dYWJDXSZe1jfdjFw0p7guwCoTR9JFKkNtiW eDul1LxGXdCUWKrkmhhQFhkbgd3BTRgT/24DVLeSmEiS+6OhoaozrArRWatDyE52 AVDpHTHBTrQfLSSBzCs9g7a88oKNUw== =hwgR -----END PGP SIGNATURE----- --XfdkZiGWe4GpXgPyF3Eq71MC2ms5K2wwq--