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Message-ID: <0be85ad4-f0d9-a5c7-e7bc-c546558df835@suse.com> Date: Thu, 16 Mar 2023 15:03:42 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH v3 1/6] xen: add reference counter support Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu , Volodymyr Babchuk References: <20230314205612.3703668-1-volodymyr_babchuk@epam.com> <20230314205612.3703668-2-volodymyr_babchuk@epam.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR2P281CA0059.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:93::13) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|DB8PR04MB7130:EE_ X-MS-Office365-Filtering-Correlation-Id: f7d057b5-2e14-4112-857c-08db2627412e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Not "at least", but strictly that way for any new code. Patches to convert various existing code to SPDX are already pending iirc. >> +#ifndef __XEN_REFCNT_H__ >> +#define __XEN_REFCNT_H__ >> + >> +#include >> +#include >> + >> +#define REFCNT_SATURATED (INT_MIN / 2) >> + >> +typedef struct { >> + atomic_t refcnt; >> +} refcnt_t; >> + >> +static inline void refcnt_init(refcnt_t *refcnt) >> +{ >> + atomic_set(&refcnt->refcnt, 1); >> +} >> + >> +static inline int refcnt_read(refcnt_t *refcnt) > > const. > >> +{ >> + return atomic_read(&refcnt->refcnt); >> +} >> + >> +static inline void refcnt_get(refcnt_t *refcnt) >> +{ >> + int old = atomic_add_unless(&refcnt->refcnt, 1, 0); >> + >> + if ( unlikely(old < 0) || unlikely (old + 1 < 0) ) > ^ extra space > > You want a single unlikely for both conditions. Are you sure? My experience was generally the other way around: likely() and unlikely() become ineffectual as soon as the compiler needs more than one branch for the inner construct (ie generally for and && or ||). Jan