From patchwork Fri May 28 18:44:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Atish Patra X-Patchwork-Id: 12287393 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-21.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E349BC4708D for ; Fri, 28 May 2021 18:45:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA95B613F6 for ; Fri, 28 May 2021 18:45:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229520AbhE1SrM (ORCPT ); Fri, 28 May 2021 14:47:12 -0400 Received: from esa3.hgst.iphmx.com ([216.71.153.141]:48410 "EHLO esa3.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229707AbhE1Sqh (ORCPT ); Fri, 28 May 2021 14:46:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=wdc.com; i=@wdc.com; q=dns/txt; s=dkim.wdc.com; t=1622227501; x=1653763501; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=3JnF6l2PLa1hy2YhPne+rwznydAel8kHIfLwnsglFNc=; b=TY60yvp/wxZo6O4ljfQWfsd7YMkpVo9hrPJI3Pz9nfvNpu6l1wCaND/r 475wdfVzkQJgIjByq0sRbizE2OmvFBsOqOp80rX4AJuXAWA/9GWFDArnk TXnOf/TBxh7dhoe/zKFOLGwApL5vTQP2ovezRmekH6CKoBLJBij0P2NVZ tm4JhsMovISePN8E6hUpT/ANd/dgQyOQS0TZvibKqqeaNmpiGJOHqm4wn 62HCwomzq6nVfZacW6nqJYoKAdVRm6Y4TyGF1GaZC/wRQw/4phoyoieCO HhBD3rjGI2KccpbN+c+gWhQ8u6nYVwXUnAB9BfgO6ll4gOrPoOIMD7lPQ Q==; IronPort-SDR: JC5CDH0cCyos98KszJHJwf9QXvDyvJhcrlg7Po0A3GLMy5SZAngXI5gVvnEfIK0OsET7Ovs6qF ydwZQFiBQnc6Mnfkujfa/haxvoZkNdefG4594Flj4MK718vRyET3L+RblGZbo2af+xLSIUEsvc MzxPuUTvUSOFplwd5YIUQIfJ8gsHoTCN0MoJ+8HgFgHGZUqLkBA+FXUMI9R25pA/pNSrO8D1NH nSqiQjjZ/a4Q27eTbiiCOINybCtN3V3WQTV0arpR64q4N0QmiiWlRHnDZYhRTuRrPbMFkxBQFF b+s= X-IronPort-AV: E=Sophos;i="5.83,230,1616428800"; d="scan'208";a="174577244" Received: from uls-op-cesaip01.wdc.com (HELO uls-op-cesaep01.wdc.com) ([199.255.45.14]) by ob1.hgst.iphmx.com with ESMTP; 29 May 2021 02:45:01 +0800 IronPort-SDR: w4dgIzm8lvZ60HYQsd3SaX3KfWgD+9xL5ig2/4X3ghZN+iFPrLbKZPgRsGR038JgLh4O4kU5Az ta8jPUDuAoTtxkdTlVMUd9IaXrrDScG+bUdegaA+Ixvx/1P2S1CPlfYWAXIC+i8wMnhGOUfvBh dR6aWwXDvdIZ9iSujAQ4jfYYuC0RJMt83MRM1S8Z6BKxvyuzsAJxn6jehCZQPS05dlTTHcliMc N3/4Pzc/I1evtSSyGbQAJ6MhSPaAyRlqj5FYAEanl1B93oP+PiK34o0hg9VvksBR2/SmlatUw8 6RDJqc/6IU5a/FDfCCpeUINa Received: from uls-op-cesaip02.wdc.com ([10.248.3.37]) by uls-op-cesaep01.wdc.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 May 2021 11:24:24 -0700 IronPort-SDR: igzx8ssNtnkSffzQ27r/mJQLZnwcef0zQB3xgf3FLZy78ZTeiKOh1/eUZk/ZSkA69WGGECj+h6 soHiShGGW/ZsPYwqnOW6i8dvgiUsxj6CBwBDa+2L7Zy/e1Cq5e8ZI8SzktfW5iUaF/R1CDiAii cjiCgot3xrrSgJfkLSjE2JUShGdgB+SuysaBylBxhTFcCw9HNGl1xliVkrhUgcOy1VhpD0bRE8 wt9OoAHSJcb2Q/F2kpfUfgN50Qd79z5tRcYqXzuqHOznNCeXaDAzuIILZAuihxgO2mEWB1XlDv Um0= WDCIronportException: Internal Received: from unknown (HELO jedi-01.wdc.com) ([10.225.163.91]) by uls-op-cesaip02.wdc.com with ESMTP; 28 May 2021 11:44:57 -0700 From: Atish Patra To: linux-kernel@vger.kernel.org Cc: Atish Patra , Anup Patel , bpf@vger.kernel.org, Daniel Lezcano , Guo Ren , Heinrich Schuchardt , Kefeng Wang , linux-doc@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org, Nick Kossifidis , Palmer Dabbelt , Paul Walmsley , Alan Kao , Nick Hu , Vincent Chen Subject: [RFC v2 7/7] Documentation: riscv: Remove the old documentation Date: Fri, 28 May 2021 11:44:05 -0700 Message-Id: <20210528184405.1793783-8-atish.patra@wdc.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210528184405.1793783-1-atish.patra@wdc.com> References: <20210528184405.1793783-1-atish.patra@wdc.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-State: RFC The existing pmu documentation describes the limitation of perf infrastructure in RISC-V ISA and limited feature set of perf in RISC-V. However, SBI PMU extension and sscofpmf extension(ISA extension) allows to implement most of the required features of perf. Remove the old documentation which is not accurate anymore. Signed-off-by: Atish Patra --- Documentation/riscv/pmu.rst | 255 ------------------------------------ 1 file changed, 255 deletions(-) delete mode 100644 Documentation/riscv/pmu.rst diff --git a/Documentation/riscv/pmu.rst b/Documentation/riscv/pmu.rst deleted file mode 100644 index acb216b99c26..000000000000 --- a/Documentation/riscv/pmu.rst +++ /dev/null @@ -1,255 +0,0 @@ -=================================== -Supporting PMUs on RISC-V platforms -=================================== - -Alan Kao , Mar 2018 - -Introduction ------------- - -As of this writing, perf_event-related features mentioned in The RISC-V ISA -Privileged Version 1.10 are as follows: -(please check the manual for more details) - -* [m|s]counteren -* mcycle[h], cycle[h] -* minstret[h], instret[h] -* mhpeventx, mhpcounterx[h] - -With such function set only, porting perf would require a lot of work, due to -the lack of the following general architectural performance monitoring features: - -* Enabling/Disabling counters - Counters are just free-running all the time in our case. -* Interrupt caused by counter overflow - No such feature in the spec. -* Interrupt indicator - It is not possible to have many interrupt ports for all counters, so an - interrupt indicator is required for software to tell which counter has - just overflowed. -* Writing to counters - There will be an SBI to support this since the kernel cannot modify the - counters [1]. Alternatively, some vendor considers to implement - hardware-extension for M-S-U model machines to write counters directly. - -This document aims to provide developers a quick guide on supporting their -PMUs in the kernel. The following sections briefly explain perf' mechanism -and todos. - -You may check previous discussions here [1][2]. Also, it might be helpful -to check the appendix for related kernel structures. - - -1. Initialization ------------------ - -*riscv_pmu* is a global pointer of type *struct riscv_pmu*, which contains -various methods according to perf's internal convention and PMU-specific -parameters. One should declare such instance to represent the PMU. By default, -*riscv_pmu* points to a constant structure *riscv_base_pmu*, which has very -basic support to a baseline QEMU model. - -Then he/she can either assign the instance's pointer to *riscv_pmu* so that -the minimal and already-implemented logic can be leveraged, or invent his/her -own *riscv_init_platform_pmu* implementation. - -In other words, existing sources of *riscv_base_pmu* merely provide a -reference implementation. Developers can flexibly decide how many parts they -can leverage, and in the most extreme case, they can customize every function -according to their needs. - - -2. Event Initialization ------------------------ - -When a user launches a perf command to monitor some events, it is first -interpreted by the userspace perf tool into multiple *perf_event_open* -system calls, and then each of them calls to the body of *event_init* -member function that was assigned in the previous step. In *riscv_base_pmu*'s -case, it is *riscv_event_init*. - -The main purpose of this function is to translate the event provided by user -into bitmap, so that HW-related control registers or counters can directly be -manipulated. The translation is based on the mappings and methods provided in -*riscv_pmu*. - -Note that some features can be done in this stage as well: - -(1) interrupt setting, which is stated in the next section; -(2) privilege level setting (user space only, kernel space only, both); -(3) destructor setting. Normally it is sufficient to apply *riscv_destroy_event*; -(4) tweaks for non-sampling events, which will be utilized by functions such as - *perf_adjust_period*, usually something like the follows:: - - if (!is_sampling_event(event)) { - hwc->sample_period = x86_pmu.max_period; - hwc->last_period = hwc->sample_period; - local64_set(&hwc->period_left, hwc->sample_period); - } - -In the case of *riscv_base_pmu*, only (3) is provided for now. - - -3. Interrupt ------------- - -3.1. Interrupt Initialization - -This often occurs at the beginning of the *event_init* method. In common -practice, this should be a code segment like:: - - int x86_reserve_hardware(void) - { - int err = 0; - - if (!atomic_inc_not_zero(&pmc_refcount)) { - mutex_lock(&pmc_reserve_mutex); - if (atomic_read(&pmc_refcount) == 0) { - if (!reserve_pmc_hardware()) - err = -EBUSY; - else - reserve_ds_buffers(); - } - if (!err) - atomic_inc(&pmc_refcount); - mutex_unlock(&pmc_reserve_mutex); - } - - return err; - } - -And the magic is in *reserve_pmc_hardware*, which usually does atomic -operations to make implemented IRQ accessible from some global function pointer. -*release_pmc_hardware* serves the opposite purpose, and it is used in event -destructors mentioned in previous section. - -(Note: From the implementations in all the architectures, the *reserve/release* -pair are always IRQ settings, so the *pmc_hardware* seems somehow misleading. -It does NOT deal with the binding between an event and a physical counter, -which will be introduced in the next section.) - -3.2. IRQ Structure - -Basically, a IRQ runs the following pseudo code:: - - for each hardware counter that triggered this overflow - - get the event of this counter - - // following two steps are defined as *read()*, - // check the section Reading/Writing Counters for details. - count the delta value since previous interrupt - update the event->count (# event occurs) by adding delta, and - event->hw.period_left by subtracting delta - - if the event overflows - sample data - set the counter appropriately for the next overflow - - if the event overflows again - too frequently, throttle this event - fi - fi - - end for - -However as of this writing, none of the RISC-V implementations have designed an -interrupt for perf, so the details are to be completed in the future. - -4. Reading/Writing Counters ---------------------------- - -They seem symmetric but perf treats them quite differently. For reading, there -is a *read* interface in *struct pmu*, but it serves more than just reading. -According to the context, the *read* function not only reads the content of the -counter (event->count), but also updates the left period to the next interrupt -(event->hw.period_left). - -But the core of perf does not need direct write to counters. Writing counters -is hidden behind the abstraction of 1) *pmu->start*, literally start counting so one -has to set the counter to a good value for the next interrupt; 2) inside the IRQ -it should set the counter to the same resonable value. - -Reading is not a problem in RISC-V but writing would need some effort, since -counters are not allowed to be written by S-mode. - - -5. add()/del()/start()/stop() ------------------------------ - -Basic idea: add()/del() adds/deletes events to/from a PMU, and start()/stop() -starts/stop the counter of some event in the PMU. All of them take the same -arguments: *struct perf_event *event* and *int flag*. - -Consider perf as a state machine, then you will find that these functions serve -as the state transition process between those states. -Three states (event->hw.state) are defined: - -* PERF_HES_STOPPED: the counter is stopped -* PERF_HES_UPTODATE: the event->count is up-to-date -* PERF_HES_ARCH: arch-dependent usage ... we don't need this for now - -A normal flow of these state transitions are as follows: - -* A user launches a perf event, resulting in calling to *event_init*. -* When being context-switched in, *add* is called by the perf core, with a flag - PERF_EF_START, which means that the event should be started after it is added. - At this stage, a general event is bound to a physical counter, if any. - The state changes to PERF_HES_STOPPED and PERF_HES_UPTODATE, because it is now - stopped, and the (software) event count does not need updating. - - - *start* is then called, and the counter is enabled. - With flag PERF_EF_RELOAD, it writes an appropriate value to the counter (check - previous section for detail). - Nothing is written if the flag does not contain PERF_EF_RELOAD. - The state now is reset to none, because it is neither stopped nor updated - (the counting already started) - -* When being context-switched out, *del* is called. It then checks out all the - events in the PMU and calls *stop* to update their counts. - - - *stop* is called by *del* - and the perf core with flag PERF_EF_UPDATE, and it often shares the same - subroutine as *read* with the same logic. - The state changes to PERF_HES_STOPPED and PERF_HES_UPTODATE, again. - - - Life cycle of these two pairs: *add* and *del* are called repeatedly as - tasks switch in-and-out; *start* and *stop* is also called when the perf core - needs a quick stop-and-start, for instance, when the interrupt period is being - adjusted. - -Current implementation is sufficient for now and can be easily extended to -features in the future. - -A. Related Structures ---------------------- - -* struct pmu: include/linux/perf_event.h -* struct riscv_pmu: arch/riscv/include/asm/perf_event.h - - Both structures are designed to be read-only. - - *struct pmu* defines some function pointer interfaces, and most of them take - *struct perf_event* as a main argument, dealing with perf events according to - perf's internal state machine (check kernel/events/core.c for details). - - *struct riscv_pmu* defines PMU-specific parameters. The naming follows the - convention of all other architectures. - -* struct perf_event: include/linux/perf_event.h -* struct hw_perf_event - - The generic structure that represents perf events, and the hardware-related - details. - -* struct riscv_hw_events: arch/riscv/include/asm/perf_event.h - - The structure that holds the status of events, has two fixed members: - the number of events and the array of the events. - -References ----------- - -[1] https://github.com/riscv/riscv-linux/pull/124 - -[2] https://groups.google.com/a/groups.riscv.org/forum/#!topic/sw-dev/f19TmCNP6yA