Messages in this thread | | | Date | Wed, 21 Sep 2022 17:36:42 +0100 | From | Jonathan Cameron <> | Subject | Re: [RFC PATCH 1/9] cxl/mem: Implement Get Event Records command |
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On Tue, 20 Sep 2022 15:10:26 -0700 Ira Weiny <ira.weiny@intel.com> wrote:
> On Tue, Sep 20, 2022 at 01:23:29PM -0700, Jiang, Dave wrote: > > > > On 9/20/2022 8:49 AM, Jonathan Cameron wrote: > > > On Fri, 9 Sep 2022 13:53:55 -0700 > > > Ira Weiny <ira.weiny@intel.com> wrote: > > > > > > > On Thu, Sep 08, 2022 at 01:52:40PM +0100, Jonathan Cameron wrote: > > > > [snip] > > > > > > > > > > > > diff --git a/include/trace/events/cxl-events.h b/include/trace/events/cxl-events.h > > > > > > > > new file mode 100644 > > > > > > > > index 000000000000..f4baeae66cf3 > > > > > > > > --- /dev/null > > > > > > > > +++ b/include/trace/events/cxl-events.h > > > > > > > > @@ -0,0 +1,127 @@ > > > > > > > > +/* SPDX-License-Identifier: GPL-2.0 */ > > > > > > > > +#undef TRACE_SYSTEM > > > > > > > > +#define TRACE_SYSTEM cxl_events > > > > > > > > + > > > > > > > > +#if !defined(_CXL_TRACE_EVENTS_H) || defined(TRACE_HEADER_MULTI_READ) > > > > > > > > +#define _CXL_TRACE_EVENTS_H > > > > > > > > + > > > > > > > > +#include <linux/tracepoint.h> > > > > > > > > + > > > > > > > > +#define EVENT_LOGS \ > > > > > > > > + EM(CXL_EVENT_TYPE_INFO, "Info") \ > > > > > > > > + EM(CXL_EVENT_TYPE_WARN, "Warning") \ > > > > > > > > + EM(CXL_EVENT_TYPE_FAIL, "Failure") \ > > > > > > > > + EM(CXL_EVENT_TYPE_FATAL, "Fatal") \ > > > > > > > > + EMe(CXL_EVENT_TYPE_MAX, "<undefined>") > > > > > > > Hmm. 4 is defined in CXL 3.0, but I'd assume we won't use tracepoints for > > > > > > > dynamic capacity events so I guess it doesn't matter. > > > > > > I'm not sure why you would say that. I anticipate some user space daemon > > > > > > requiring these events to set things up. > > > > > Certainly a possible solution. I'd kind of expect a more hand shake based approach > > > > > than a tracepoint. Guess we'll see :) > > > > Yea I think we should wait an see. > > > > > > > > > > > > + { CXL_EVENT_RECORD_FLAG_PERF_DEGRADED, "Performance Degraded" }, \ > > > > > > > > + { CXL_EVENT_RECORD_FLAG_HW_REPLACE, "Hardware Replacement Needed" } \ > > > > > > > > +) > > > > > > > > + > > > > > > > > +TRACE_EVENT(cxl_event, > > > > > > > > + > > > > > > > > + TP_PROTO(const char *dev_name, enum cxl_event_log_type log, > > > > > > > > + struct cxl_event_record_raw *rec), > > > > > > > > + > > > > > > > > + TP_ARGS(dev_name, log, rec), > > > > > > > > + > > > > > > > > + TP_STRUCT__entry( > > > > > > > > + __string(dev_name, dev_name) > > > > > > > > + __field(int, log) > > > > > > > > + __array(u8, id, UUID_SIZE) > > > > > > > > + __field(u32, flags) > > > > > > > > + __field(u16, handle) > > > > > > > > + __field(u16, related_handle) > > > > > > > > + __field(u64, timestamp) > > > > > > > > + __array(u8, data, EVENT_RECORD_DATA_LENGTH) > > > > > > > > + __field(u8, length) > > > > > > > Do we want the maintenance operation class added in Table 8-42 from CXL 3.0? > > > > > > > (only noticed because I happen to have that spec revision open rather than 2.0). > > > > > > Yes done. > > > > > > > > > > > > There is some discussion with Dan regarding not decoding anything and letting > > > > > > user space take care of it all. I think this shows a valid reason Dan > > > > > > suggested this. > > > > > I like being able to print tracepoints with out userspace tools. > > > > > This also enforces structure and stability of interface which I like. > > > > I tend to agree with you. > > > > > > > > > Maybe a raw tracepoint or variable length trailing buffer to pass > > > > > on what we don't understand? > > > > I've already realized that we need to print all reserved fields for this > > > > reason. If there is something the kernel does not understand user space can > > > > just figure it out on it's own. > > > > > > > > Sound reasonable? > > > Hmm. Printing reserved fields would be unusual. Not sure what is done for similar > > > cases elsewhere, CPER records etc... > > > > > > We could just print a raw array of the whole event as well as decode version, but > > > that means logging most of the fields twice... > > > > > > Not nice either. > > > > > > I'm a bit inclined to say we should maybe just ignore stuff we don't know about or > > > is there a version number we can use to decide between decoded vs decoded as much as > > > possible + raw log? > > I'm not a fan of loging the raw + decoded versions. > > > > > libtraceevent can pull the trace event data structure fields directly. So > > the raw data can be pulled directly from the kernel. > > This raw data needs to be in a field though. If the kernel does not save the > reserved fields in the TP_fast_assign() then the data won't be in a field to > access. > > > > > And what gets printed > > to the trace buffer can be decoded data constructed from those fields by the > > kernel code. So with that you can have access both. > > > > Fast assigning the entire buffer + decoded versions will roughly double the > trace event size. > > Thinking through this a bit more there is a sticking point. > > The difficulty will be ensuring that any new field names are documented such > that when user space starts to look at them they can determine if that data > appears as a new field or as part of a reserved field. > > For example if user space needs to access data in the reserved data now it can > simply decode it. However, when that data becomes a field it no longer is part > of the reserved data. So what user space would need to do is look for the > field first (ie know the field name) and then if it does not appear extract it > from the reserved data. > > I'm now wondering if I've wasted my time decoding anything since the kernel > does not need to know anything about these fields. Because the above scenario > means that user space may get ugly over time. > > That said I don't think it will present any incompatibilities. So perhaps we > are ok?
I favor decoding current record in kernel and packing it appropriately. If that means we don't provide some new data from a future version then such is life - the kernel needs upgrading. That information is unlikely to be crucial - it's probably just more detail.
Jonathan
> > Ira
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