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Wed, 1 Jul 2020 07:52:51 +0000 From: Johannes Thumshirn To: Hongnan Li , "linux-block@vger.kernel.org" CC: "axboe@kernel.dk" Subject: Re: [PATCH] blk-iolatency:postpone ktime_get() execution until blk_iolatency_enabled() return true Thread-Topic: [PATCH] blk-iolatency:postpone ktime_get() execution until blk_iolatency_enabled() return true Thread-Index: AQHWT22cn+7v9KB7YEGn59MYBJ9tBA== Date: Wed, 1 Jul 2020 07:52:51 +0000 Message-ID: References: <1593583467-18945-1-git-send-email-hongnan.li@linux.alibaba.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: linux.alibaba.com; dkim=none (message not signed) header.d=none;linux.alibaba.com; dmarc=none action=none header.from=wdc.com; x-originating-ip: [2001:a62:1515:bd01:115:56a6:c821:2683] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 8f8bc7b4-d40a-491e-c378-08d81d93c193 x-ms-traffictypediagnostic: SN6PR04MB4239: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:901; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SN4PR0401MB3598.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 8f8bc7b4-d40a-491e-c378-08d81d93c193 X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Jul 2020 07:52:51.7010 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: z5yu6zMWgUlco3yTcyc48YiouLwpUafXQU8nnFZWhmcwRNqXgq9VgIrYtL6EvGEaS/9HaLU+GukkRBoXFx0DNmnD2Wi45HKAHUsio+TY5Rw= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR04MB4239 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 01/07/2020 08:05, Hongnan Li wrote:=0A= > ktime_to_ns(ktime_get()) which is expensive do not need to be executed if= =0A= > blk_iolatency_enabled() return false in blkcg_iolatency_done_bio().=0A= > Postponing ktime_to_ns(ktime_get()) execution can reduce CPU usage=0A= > when blk_iolatency was disabled.=0A= > =0A= > Signed-off-by: Hongnan Li =0A= > ---=0A= > block/blk-iolatency.c | 3 ++-=0A= > 1 file changed, 2 insertions(+), 1 deletion(-)=0A= > =0A= > diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c=0A= > index c128d50..8c1487e 100644=0A= > --- a/block/blk-iolatency.c=0A= > +++ b/block/blk-iolatency.c=0A= > @@ -591,7 +591,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *r= qos, struct bio *bio)=0A= > struct rq_wait *rqw;=0A= > struct iolatency_grp *iolat;=0A= > u64 window_start;=0A= > - u64 now =3D ktime_to_ns(ktime_get());=0A= > +=0A= > bool issue_as_root =3D bio_issue_as_root_blkg(bio);=0A= > bool enabled =3D false;=0A= > int inflight =3D 0;=0A= > @@ -608,6 +608,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *r= qos, struct bio *bio)=0A= > if (!enabled)=0A= > return;=0A= > =0A= > + u64 now =3D ktime_to_ns(ktime_get());=0A= > while (blkg && blkg->parent) {=0A= > iolat =3D blkg_to_lat(blkg);=0A= > if (!iolat) {=0A= > =0A= =0A= You're mixing declarations and code.=0A= =0A= please do=0A= - u64 now =3D ktime_to_ns(ktime_get());=0A= + u64 now;=0A= =0A= [...]=0A= + now =3D ktime_to_ns(ktime_get());=0A=