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libpfm_amd64

NAME

libpfm_amd64 - support for AMD64 processors

SYNOPSIS

 #include <perfmon/pfmlib.h>
 #include <perfmon/pfmlib_amd64.h>
 
 

 

DESCRIPTION

The libpfm library provides full support for the AMD64 processor families 0Fh and 10H (K8, Barcelona, Phenom) when running in either 32-bit or 64-bit mode. The interface is defined in pfmlib_amd64.h. It consists of a set of functions and structures which describe and allow access to the AMD64 specific PMU features. Note that it only supports AMD processors.

When AMD64 processor-specific features are needed to support a measurement, their descriptions must be passed as model-specific input arguments to the pfm_dispatch_events() function. The AMD64 processor-specific input arguments are described in the pfmlib_amd64_input_param_t structure and the output parameters in pfmlib_amd64_output_param_t. They are defined as follows:

 typedef struct {
         uint32_t        cnt_mask;
         uint32_t        flags;
 } pfmlib_amd64_counter_t;
 
 typedef struct {
         unsigned int maxcnt;
         unsigned int options;
 } ibs_param_t;
 
 typedef struct {
         pfmlib_amd64_counter_t pfp_amd64_counters[PMU_AMD64_MAX_COUNTERS];
         uint32_t        flags;
         uint32_t        reserved1;
         ibs_param_t     ibsfetch;
         ibs_param_t     ibsop;
         uint64_t        reserved2;
 } pfmlib_amd64_input_param_t;
 
 typedef struct {
         uint32_t        ibsfetch_base;
         uint32_t        ibsop_base;
         uint64_t        reserved[7];
 } pfmlib_amd64_output_param_t;
 

The flags field of pfmlib_amd64_input_param_t describes which features of the PMU to use. Following use flags exist:

PFMLIB_AMD64_USE_IBSFETCH

Profile IBS fetch performance (see below under INSTRUCTION BASED SAMPLING)

PFMLIB_AMD64_USE_IBSOP

Profile IBS execution performance (see below under INSTRUCTION BASED SAMPLING)

Multiple features can be selected. Note that there are no use flags needed for ADDITIONAL PER-EVENT FEATURES.

Various typedefs for MSR encoding and decoding are available. See pfmlib_amd64.h for details.

ADDITIONAL PER-EVENT FEATURES

AMD64 processors provide a few additional per-event features for counters: thresholding, inversion, edge detection, virtualization. They can be set using the pfp_amd64_counters data structure for each event. The flags field of pfmlib_amd64_counter_t can be initialized as follows:

PFMLIB_AMD64_SEL_INV

Inverse the results of the cnt_mask comparison when set

PFMLIB_AMD64_SEL_EDGE

Enables edge detection of events.

PFMLIB_AMD64_SEL_GUEST

On AMD64 Family 10h processors only. Event is only measured when processor is in guest mode.

PFMLIB_AMD64_SEL_HOST

On AMD64 Family 10h processors only. Event is only measured when processor is in host mode.

The cnt_mask field is used to set the event threshold. The value of the counter is incremented each time the number of occurrences per cycle of the event is greater or equal to the value of the field. When zero all occurrences are counted.

INSTRUCTION BASED SAMPLING (IBS)

The libpfm_amd64 provides access to the model specific feature Instruction Based Sampling (IBS). IBS has been introduced with family 10h.

The IBS setup is using the structures pfmlib_amd64_input_param_t and pfmlib_amd64_output_param_t with its members flags, ibsfetch, ibsop, ibsfetch_base, ibsop_base. The input arguments ibsop and ibsfetch can be set in inp_mod (type pfmlib_amd64_input_param_t). The corresponding flags must be set to enable a feature.

Both, IBS execution profiling and IBS fetch profiling, require a maximum count value of the periodic counter (maxcnt) as parameter. This is a 20 bit value, bits 3:0 are always set to zero. Additionally, there is an option (options) to enable randomization (IBS_OPTIONS_RANDEN) for IBS fetch profiling.

The IBS registers IbsFetchCtl (0xC0011030) and IbsOpCtl (0xC0011033) are available as PMC and PMD in Perfmon. The function pfm_dispatch_events() initializes these registers according to the input parameters in pfmlib_amd64_input_param_t.

Also, pfm_dispatch_events() passes back the index in pfp_pmds[] of the IbsOpCtl and IbsFetchCtl register. For this there are the entries ibsfetch_base and ibsop_base in pfmlib_amd64_output_param_t. The index may vary depending on other PMU settings, especially counter settings. If using the PMU with only one IBS feature and no counters, the index of the base register is 0.

Example code:

         /* initialize IBS */
         inp_mod.ibsop.maxcnt = 0xFFFF0;
         inp_mod.flags |= PFMLIB_AMD64_USE_IBSOP;
         ret = pfm_dispatch_events(NULL, &inp_mod, &outp, &outp_mod);
         if (ret != PFMLIB_SUCCESS) { ... }
 
         /* setup PMU */
         /* PMC_IBSOPCTL */
         pc[0].reg_num   = outp.pfp_pmcs[0].reg_num;
         pc[0].reg_value = outp.pfp_pmcs[0].reg_value;
         /* PMD_IBSOPCTL */
         pd[0].reg_num   = outp.pfp_pmds[0].reg_num;
         pd[0].reg_value = 0;
 
         /* setup sampling */
         pd[0].reg_flags = PFM_REGFL_OVFL_NOTIFY;
         /* add range check here */
         pd[0].reg_smpl_pmds[0] =
                 ((1UL << PMD_IBSOP_NUM) - 1) << outp.pfp_pmds[0].reg_num;
 
         /* write pc and pd to PMU */
         ...
 

ERRORS

Refer to the description of the pfm_dispatch_events() function for errors.

SEE ALSO

pfm_dispatch_events(3) and set of examples shipped with the library

AUTHORS

 Stephane Eranian <eranian@gmail.com>
 Robert Richter <robert.richter@amd.com>