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charset="us-ascii" Content-ID: MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 469cd46f-dc05-4fdb-eb6d-08d96e65ebea X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Sep 2021 23:03:47.6378 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: o25N0FS2Vb59SoINjv3Jgm1W3Z41sc+NhMZZBtfTtjuY/T2s2fgUyPsZKSJDd2Rlx3ER/N8oiD+WLwjcmUNvRA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR15MB5109 X-OriginatorOrg: fb.com X-Proofpoint-GUID: -S1dzygUkH1OrtVaCqEilaFX5ma5d-vX X-Proofpoint-ORIG-GUID: -S1dzygUkH1OrtVaCqEilaFX5ma5d-vX X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-09-02_04:2021-09-02,2021-09-02 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 mlxscore=0 bulkscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 phishscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2108310000 definitions=main-2109020133 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Sep 2, 2021, at 3:53 PM, Andrii Nakryiko wrote: > > On Thu, Sep 2, 2021 at 9:58 AM Song Liu wrote: >> >> Introduce bpf_get_branch_snapshot(), which allows tracing pogram to get >> branch trace from hardware (e.g. Intel LBR). To use the feature, the >> user need to create perf_event with proper branch_record filtering >> on each cpu, and then calls bpf_get_branch_snapshot in the bpf function. >> On Intel CPUs, VLBR event (raw event 0x1b00) can be use for this. >> >> Signed-off-by: Song Liu >> --- >> include/uapi/linux/bpf.h | 22 ++++++++++++++++++++++ >> kernel/bpf/trampoline.c | 3 ++- >> kernel/trace/bpf_trace.c | 33 +++++++++++++++++++++++++++++++++ >> tools/include/uapi/linux/bpf.h | 22 ++++++++++++++++++++++ >> 4 files changed, 79 insertions(+), 1 deletion(-) >> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index 791f31dd0abee..c986e6fad5bc0 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h >> @@ -4877,6 +4877,27 @@ union bpf_attr { >> * Get the struct pt_regs associated with **task**. >> * Return >> * A pointer to struct pt_regs. >> + * >> + * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags) >> + * Description >> + * Get branch trace from hardware engines like Intel LBR. The >> + * branch trace is taken soon after the trigger point of the >> + * BPF program, so it may contain some entries after the > > This part is a leftover from previous design, so not relevant anymore? Hmm.. This is still relevant, but not very accurate. I guess we should provide more information, like "For more information about branches before the trigger point, this should be called early in the BPF program". Song > >> + * trigger point. The user need to filter these entries >> + * accordingly. >> + * >> + * The data is stored as struct perf_branch_entry into output >> + * buffer *entries*. *size* is the size of *entries* in bytes. >> + * *flags* is reserved for now and must be zero. >> + * >> + * Return >> + * On success, number of bytes written to *buf*. On error, a >> + * negative value. >> + * >> + * **-EINVAL** if arguments invalid or **size** not a multiple >> + * of **sizeof**\ (**struct perf_branch_entry**\ ). >> + * >> + * **-ENOENT** if architecture does not support branch records. > > [...]