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([2a02:8084:e84:2480:228:f8ff:fe6f:83a8]) by smtp.gmail.com with ESMTPSA id s8sm458703wrg.50.2020.06.10.09.24.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jun 2020 09:24:58 -0700 (PDT) Subject: Re: [PATCH v2 2/3] serial: core: fix sysrq overhead regression To: Johan Hovold , Greg Kroah-Hartman Cc: Jiri Slaby , Andy Shevchenko , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200610152232.16925-1-johan@kernel.org> <20200610152232.16925-3-johan@kernel.org> From: Dmitry Safonov <0x7f454c46@gmail.com> Message-ID: <19008afb-bfbb-35e2-3bd5-e7fd1b7355cc@gmail.com> Date: Wed, 10 Jun 2020 17:24:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200610152232.16925-3-johan@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Hi Johan, On 6/10/20 4:22 PM, Johan Hovold wrote: > Commit 8e20fc391711 ("serial_core: Move sysrq functions from header > file") converted the inline sysrq helpers to exported functions which > are now called for every received character, interrupt and break signal > also on systems without CONFIG_MAGIC_SYSRQ_SERIAL instead of being > optimised away by the compiler. The part with ifdeffing looks good to me. > Inlining these helpers again also avoids the function call overhead when > CONFIG_MAGIC_SYSRQ_SERIAL is enabled (e.g. when the port is not used as > a console). But this one, coul you add measures? (it will also help to understand if it's a stable material). If one function call actually matters here, than should uart_insert_char() also go into header? I see quite common pattern in drivers: : if (!uart_handle_sysrq_char(&up->port, ch)) : uart_insert_char(&up->port, byte, 0, ch, TTY_NORMAL); Don't misunderstand me, but I would prefer keeping headers cleaner without realization details with the exception if function calls actually hurts the performance. Probably, a comment like /* * Keeping these functions in the header improves performance by X% on * YYY platform by letting the compiler inline them. */ would also help. Thanks for working on this, Dmitry