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Rozycki" Cc: Paul Walmsley , Palmer Dabbelt , Huacai Chen , WANG Xuerui , Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , Alexandre Ghiti , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev Subject: Re: [PATCH 1/4] riscv: entry: Convert ret_from_fork() to C Message-ID: References: <20250122-riscv_optimize_entry-v1-0-4ee95559cfd0@rivosinc.com> <20250122-riscv_optimize_entry-v1-1-4ee95559cfd0@rivosinc.com> 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-20250127_125544_924988_3C6FBD2B X-CRM114-Status: GOOD ( 14.18 ) X-BeenThere: linux-riscv@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-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, Jan 27, 2025 at 08:20:56PM +0000, Maciej W. Rozycki wrote: > On Sun, 26 Jan 2025, Charlie Jenkins wrote: > > > > Wouldn't it make sense to save a jump here and make it a tail call, i.e.: > > > > > > la ra, ret_from_exception > > > tail ret_from_fork > > > > > > > I don't believe so due to the return address stack. It was shown in this > > patch [1] that a 7% performance improvement can be seen on existing > > riscv hardware by performing the extra jump. Doing tail calls should be > > avoided on riscv since the hardware can be expected to predict the > > return address incorrectly every time if the return address is manually > > changed. > > Fair enough, thanks. Though no link to said patch given. Oops! Here it is: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/. > > Maciej _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv