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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?92cj4DVhwj6FSX+u5P89SGd+LjchKKotFzSlkRQ/TuXLmUJSK2uzdH8/aqLo?= =?us-ascii?Q?IFf+ZtmuP2Bn6japLSt2ux88bHDQaj3uhyeICc1AfrU/l/sm3kmK5GM4a0tG?= =?us-ascii?Q?twPQzR0WCJ1xSBrkIFGO/nLvXI1v8RlWCMdoXM9bHnKb3meqW88etpuPC8bf?= =?us-ascii?Q?nxN9V28xy2lbEMq0xtuxB987jcEldkOFPlrA0Uh/Y9GC8BCwH0M/KiL5Hhir?= =?us-ascii?Q?tygWGfH8WRNTBJWIoYiH02sYqkzizMBf1DVhgFYno6D5P80LKkcnJazGXZL7?= =?us-ascii?Q?1vCdvK4KNm35/pI6bkk6pJLQgJ+OSvmkxhdyf4lqdvutzNsRV6g/5KOt0Pc/?= =?us-ascii?Q?MmoWgMMXSRw9CBKX9BGxNXG/glWgjQ+jFHkOTg2FcabNz8CwCGobzUicz5pl?= =?us-ascii?Q?zz4RL0aq0/L3tZbpM9z+OV+iA5I8F9ySg9sieMUtLQTztQQw7KjfX3NpR7v7?= =?us-ascii?Q?ByEJtN5aJhaMIkyrbScHOnxVyVFjFFVYgDhtrXD+hQc80LUToBIF7r221SW9?= =?us-ascii?Q?vMQ+I096Lbn0CMZ+codpcSQCSPSkIxyIdwANXEX2tPi/JHTIZ/uL87gnzRIB?= =?us-ascii?Q?jBlsoS5syB8Pcgg394SAFspXodOQyrYW4JgY99r+AJRk7LsFt7oU+UopApwF?= =?us-ascii?Q?FBhE5G8BtCtzcM5iZ6VMxGXXkwRP875X0qeZ8sKMlJYpncDInn+bkO4riIoM?= =?us-ascii?Q?gyRlvkJt316aHn84SGsUnuCYzLqxOqye/UOrIhKIiRMQiRpArVhIw6xGbgBe?= =?us-ascii?Q?1EWcU4Rh94NRvNGmVO8CWr6jWqO/TWPEiq9QGLFVYcOwhKPrzRJCOH1kpwZw?= =?us-ascii?Q?W+znobahc1kvqBlutm57d3/mCVgt67VK4n3cwz9Fwoa5V+zpv03P42CGQLry?= =?us-ascii?Q?3XHfCa9ipURY1XpCycTWdOFC4GPhm/JSWvKFIGLD6mHmXfiSz/pCZ1MMEvya?= =?us-ascii?Q?tYn2skDlPIEek4C5LshEhgsAGhBwPBbby18B9ST7cu77zaYjxWCJg5TV8ylA?= =?us-ascii?Q?OMPruCDvoWcknsfPIiiwe/+HLEmLkDFAgGFrrg1kSLj0bbPvCgOD2biNDzDe?= =?us-ascii?Q?MYqUfw552Mx2XtVKJO3/102WINWAConF1PxnU1XrRIA6/iSiFOfU+gwoEuow?= =?us-ascii?Q?93x+/DngDR5BUPYhrTe4veg2vyVQyNC+I+kCT3Dnhm21gzC0AstFrtlUgvfM?= =?us-ascii?Q?5BAGtrLe9iI6p4DweUipVtFUpt+EnJXLWOpyYcMS2BLbrvJDtu/n575BE4oG?= =?us-ascii?Q?RCZa6ngBS17Lz9jcbNXwtq0pUnBZPenNs1P5WIKaTLyeEzN31/4RwDuFcrZ9?= =?us-ascii?Q?cdEmk2t+AtGbyHai9EugGMsU7u4ftBSIcz/mbg7yHpDUGhr+PK7ieD/z8N79?= =?us-ascii?Q?U4OUlHuugHYXm+HEyElUcD7FFSHYCaehVjRZGcw7NZVkGvXJrTJRhyu35sAL?= =?us-ascii?Q?tIli49kq/sc0fztZGONKuaOHK/yn3zrntHCMNBDiPPVwynH6Q7tZktHMFuqU?= =?us-ascii?Q?VnWKZ7/t9LwIpYUgp46Ck/qeR14sEnlNDgtBl3Bf2UJBYmN2UCOhw07fGzwv?= =?us-ascii?Q?SXHhlR679WXAtRDPqn5mRbdK215p9wGvjjcI4i4SLktMBLbPJYLc5nkIoX+U?= =?us-ascii?Q?FA=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: a0aebc22-d768-48a2-2f96-08dad49b352d X-MS-Exchange-CrossTenant-AuthSource: MWHPR1101MB2126.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Dec 2022 19:27:10.7425 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: aKDEAMWa/UhR32D+QPn3HF4SBrzeRYGusZSJwEGKMF13lSNKt6mrjBLTzpM2dp1PkqeBWRjznaYIkHJ9ZwuLDVXy90QcTjNuXVMhD4QbcBg= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5142 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Steven Rostedt wrote: > On Thu, 1 Dec 2022 18:29:20 -0800 > Dan Williams wrote: > > > > static void cxl_mem_get_records_log(struct cxl_dev_state *cxlds, > > > enum cxl_event_log_type type) > > > { > > > @@ -732,13 +769,22 @@ static void cxl_mem_get_records_log(struct cxl_dev_state *cxlds, > > > } > > > > > > nr_rec = le16_to_cpu(payload->record_count); > > > - if (trace_cxl_generic_event_enabled()) { > > > + if (nr_rec > 0) { > > > int i; > > > > > > - for (i = 0; i < nr_rec; i++) > > > - trace_cxl_generic_event(dev_name(cxlds->dev), > > > - type, > > > - &payload->records[i]); > > > + if (trace_cxl_generic_event_enabled()) { > > > > Again, trace_cxl_generic_event_enabled() injects some awkward > > formatting here to micro-optimize looping. Any performance benefit this > > code might offer is likely offset by the extra human effort to read it. > > This is commonly used throughout the kernel, and highly suggested for use to > encapsulate any work being done only for tracing, when tracing is disabled. > It uses static_braches/jump_labels which makes the loop into a 'nop' when > tracing is off. That is, there is zero overhead for the for loop below (and > there's not even a branch to skip it!) > > But sure, if you really don't care as it's not a fast path, then keep it > out. I like people to keep the habit of doing this, because otherwise it > tends to creep into the fast paths. Duly noted. It makes a lot of sense when you are tracing in a fast path to skip any and all preamble code. In this case we are doing it after doing a whole series of uncached PCI mmio reads with all the stalling and serialization that implies. Speaking of which, this probably wants a cond_resched() after each loop iteration. I'll note it is also a tracepoint that is likely to be enabled most of the time in production.