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Poulose" , Anshuman Khandual , John Garry , Will Deacon , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-arm-kernel , Linux Kernel Mailing List , linux-perf-users@vger.kernel.org Subject: Re: [PATCH 2/6] perf cs-etm: Initialise architecture based on TRCIDR1 Message-ID: <20210802150358.GA148327@leoy-ThinkPad-X240s> References: <20210721090706.21523-1-james.clark@arm.com> <20210721090706.21523-3-james.clark@arm.com> <20210731060312.GB7437@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210802_080408_458404_C2ACB436 X-CRM114-Status: GOOD ( 39.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Mike, On Mon, Aug 02, 2021 at 03:04:14PM +0100, Mike Leach wrote: [...] > > > > +#define TRCIDR1_TRCARCHMIN_SHIFT 4 > > > > +#define TRCIDR1_TRCARCHMIN_MASK GENMASK(7, 4) > > > > +#define TRCIDR1_TRCARCHMIN(x) (((x) & TRCIDR1_TRCARCHMIN_MASK) >> TRCIDR1_TRCARCHMIN_SHIFT) > > > > +static enum _ocsd_arch_version cs_etm_decoder__get_arch_ver(u32 reg_idr1) > > > > +{ > > > > + /* > > > > + * If the ETM trace minor version is 4 or more then we can assume > > > > + * the architecture is ARCH_AA64 rather than just V8 > > > > + */ > > > > + return TRCIDR1_TRCARCHMIN(reg_idr1) >= 4 ? ARCH_AA64 : ARCH_V8; > > > > +} > > > > > > This is true for ETM4.x & ETE 1.x (arch 5.x) but not ETM 3.x > > > Probably need to beef up this comment or the function name to emphasise this. > > > > Yeah, I think it's good to change the function name. Eventually, this > > function should only be used for ETM4.x and ETE. > > > > Another minor comment is: can we refine the arch version number, e.g. > > change the OpenCSD's macro "ARCH_AA64" to "ARCH_V8R4", (or > > "ARCH_V8R3_AA64"), this can give more clear clue what's the ETM version. > > > > The purpose of these macros is to inform the decoder of the > architecture of the PE - not the version of the ETM. > > These OpenCSD macros are defined by the library headers > (ocsd_if_types.h) and not the perf headers. > These have been published as the API / ABI for OpenCSD and as such > changing them affects all OpenCSD clients, not just perf. I understand these macros are defined in OpenCSD lib as APIs, since I saw these macros have not been widely used in perf tool (e.g. ARCH_AA64), so this is why I think it's good to take chance to refine the naming conventions. > This PE architecture version is used along with the core profile to > determine which instructions are valid waypoint instructions to > associate with atom elements when walking the program image during > trace decode. > > From v8.3 onwards we moved away from filtering on specific > architecture versions. This was due to two factors:- > 1. The architectural rules now allow architectural features for one > increment e.g. Arch 8.4, to be backported into the previous increment > - e,g, 8.3, which made this filtering more difficult to track. > 2. After discussion with the PE architects it was clear that > instructions in a later architect version would not re-use older > opcodes from a previous one and be nop / invalid in the earlier > architectures. (certainly in the scope of AA64). Therefore > the policy in the decoder is to check for all the instructions we know > about for the latest version of architecture, even if we could be > decoding an earlier architecture version. This means we may check for > a few more opcodes than necessary for earlier version of the > architecture, but the overall decode is more robust and easier to > maintain. > > Therefore for any AA64 core beyond v8.3 - it is safe to use the > ARCH_AA64 PE architecture version and the decoder will handle it. I have no objection for current approach; but two things can cause confusions and it might be difficult for maintenance: - The first thing is now we base on the bit fields TRCIDR1::TRCARCHMIN to decide the PE architecture version. In the ETMv4 spec, TRCIDR1::TRCARCHMIN is defined as the trace unit minor version, so essentially it's a minor version number for tracer (ETM) but not the PE architecture number. But now we are using it to decide the PE architecture number (8.3, 8.4, etc...). - The second thing is the macros' naming convention. E.g. "AA64" gives me an impression it is a general naming "Arm Arch 64" for all Arm 64-bit CPUs, it's something like an abbreviation for "aarch64"; so seems to me it doesn't show any meaningful info for PE's architecture version number. This is why I proposed to use more explict macro definition for architectures (e.g. ARCH_V8R3, ARCH_V8R4, ARCH_V9R0, etc). If we really want to use ARCH_AA64, it's better to give some comments in the code. Thanks a lot for shared the background info. Leo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel