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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?azJOU7/uxdTAjWfXu9VNldhjiT9jkwv0Tm9ggGsNEHiBsRpJvTC2xHsnIdJU?= =?us-ascii?Q?4H7N+ZBQN+R1vkI1vjuGTCSKURLN3iykVTWkSnEl8GRYWVmQ2tjkYJg6StBT?= =?us-ascii?Q?+JNwvJKqPMPomSH6jt1WFrio+hATQot3ySvg3kV8HqnxJZ7I5mmacsUERpwB?= =?us-ascii?Q?R2gnqkwgDMavn/G+qgPjVuVKLB15Hf1QFa3ngz1czusiWgf5nzMXafswOcNy?= =?us-ascii?Q?euhrxZKX85WOZBqksHm9JoHBOAItSnFU+4VqyFhbDgwaeUtniz94+TSTLimS?= =?us-ascii?Q?2VR3vNdwCa+hpgRXo/OP7RGOp/Bj7evDx4kVjO3mwSHSDGpcSCOBgUwjW9Pd?= =?us-ascii?Q?slURisqsU4I2cEZOKjuaKDWXRCSSOCcUZFmYta/2BxPgj5Kyol7dfXKs9UjL?= =?us-ascii?Q?8C5A17DvCT7I67Rn0JQt2tyDdV0fRbPf2jPS2c+Fc5beknDpSwygSUMHFba6?= =?us-ascii?Q?RYchwynOEu/7e6pjdyeczgHLIElKgNZoHoGEVWGzUBdnb1Afpr5/9PXwPPgM?= =?us-ascii?Q?nZDT2xMYR5Dag8QPLC2gq1uOkbX/a8N5DGn40NYbfXhEni+Am2RrfZTgu3nL?= =?us-ascii?Q?SosYd8UPzWWxeSBjgpMF0oJgq61lekGzbnf6LgA8Kchcg66I82CLnNNW3NkS?= =?us-ascii?Q?U2/Zd5VH4q0SxC7xj5EpbfFbMMHlEjC0PFIbCoTbYvpnmOoWdMPeJcUAr73E?= =?us-ascii?Q?nXg3MzvNpHd79c8EglcBAh0mJT5xXLFsTT52Y+zItHf1CxZMttWwDtBuKTDr?= =?us-ascii?Q?yvbK7Dp6TM7oEeLKdoTbsB+8GyfbcsFv3Uact23FXUJmc/37Wi7l8QvM6bre?= =?us-ascii?Q?D27o5kn5/XLTe3wm5hjxo8SCRqenoPkwzUj+kBHYh1UK0PoRvXK3B4O4a2Lx?= =?us-ascii?Q?CbRd2QOjNI7DOa9JBVkM94b9p0OZJWlSvgnSK1z7Z3y9lhaY88QlvJpi2Nl6?= =?us-ascii?Q?dtm6tAqVhwVIPYkvUwxvFJFfihlymdt5BxJgHNZIZihd/x9KiCPBWhYs5NnE?= =?us-ascii?Q?dTx+G9SUBGWzbsfxcZsAf28hrEGxv51RXCAJJurka9LNalrwyjE/7dP0viPd?= =?us-ascii?Q?xzg+e7jD5U05QGmoIN4QGiD3OM1/CjKYZ3qSP+JNCpxXRyyM+5pK75ERaJm1?= =?us-ascii?Q?j9c582NA/d4iOvc6N4uFN07o5fOJbVsTPmhTi1fgUtg88TTFQMpn1wj3KqQz?= =?us-ascii?Q?rGtk9lZTZPRSKHTFSYPTNXdpL/MDOiHxmakP5LdgcNun59qTC1b/KRmRGUf0?= =?us-ascii?Q?pseUlU8ci1AwlouDKdLQ+zrZnGR8n5bZEaceRyA8AhRPFER1Uw398HKuO+bM?= =?us-ascii?Q?e/pvb7iszC551SfcI9S9QB9RFIZb4o261kkgffsLo9h3VYGfP58+QBNzgZC3?= =?us-ascii?Q?PoeHlTbNmTJ26ZUkxq9feK6jQv1lj2xc6wn4/6H4g8Ms2tVRBsrLkPKPiOxf?= =?us-ascii?Q?FvR1ryPN7iVtLGeC4R5e6Zl3OTsFDsU5M24CO7slZosrwgf3Gw2gACrFgnPW?= =?us-ascii?Q?xC9QCps54pAqmoZIUpp8iWgIsDsEP7Jl4UD2yaFD6+3nf48BH+NNcDIyAGYJ?= =?us-ascii?Q?WipHwzpZapuuVEILe1Fip+biz0xyhJ0QEjiTlYZ3?= X-MS-Exchange-CrossTenant-Network-Message-Id: bb684a37-6308-4f34-f6e5-08dad4ac23c8 X-MS-Exchange-CrossTenant-AuthSource: SA1PR11MB6733.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Dec 2022 21:28:22.7444 (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: 9/MVrq2Unzk9fshhZsXjeFwDtc1TB0qxoD6/NQn/AVZRs8Vb5jxpzOTL7wknY2xBX5rhXLjdjKNaxyhAHyU/Jw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR11MB6339 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 02, 2022 at 11:27:07AM -0800, Dan Williams wrote: > 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. Thanks for chiming in here Steven. I should have pushed back on this. > > 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. Ok I did not have any of these in there originally and I will remove them now. Thanks! Ira