From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2015017E; Mon, 2 Dec 2024 06:12:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733119937; cv=none; b=AhNoHxy7IbcYxtCNXuBqkFSGy/YdfyfiNDWzzwtcfumtYnEUFRST/URztocRCPOlwPgdAMLzVz8/5H4nAYBr1/6ePL8RLUvrbcRF1jXNfroUqQ8KHcp2yIhPf09HGRPzsl0hr48E9sTKxg0jsWdNPa22UWwtWKIsWY46837DtI0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733119937; c=relaxed/simple; bh=av2/qGxfETVVpYWjdPwqPFx/7HMHwabf8lIR+vBntXw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=enAPSygDprLujgAFEqW6whZUfhMdl7f9rjs5S8A5M93WuTCjqWiZpaS6jutvnt4xYVjeJOQ7F2HFbp92xoTdIpOPM8rSW7bPW9kS5g6ZbEDhycHyzd249TIj3QyOtRVr4K2cBmYzathTapElvL1cZKJsK31hYUDMsaG9q34gzmE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QniMDvTA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QniMDvTA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 999D2C4CED2; Mon, 2 Dec 2024 06:12:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1733119936; bh=av2/qGxfETVVpYWjdPwqPFx/7HMHwabf8lIR+vBntXw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QniMDvTA6GB3amtZcVS0cBYMdgTa/XN3jumFMLpoYRgh2uIPL5UR38shdNEQrKHt6 BLKq8Fh1/vfSSzDoHHDe+GpQqECknIG3CcWcCGCSF4ckdl2TzXJovcZkDb+TCsjwMm XzyquP6Ywr56hEw5d5NrksmBFNbQiWYnwFKS3rplZGVaR/yuVnH881KhniICq4T5Kz WdVvLyPBNf4xBnQTmR8Z9rFDamGVWmBlrL4OgGKfNl4zxQNIJHWFqm7RvuuUfEcR/r ruKKELR3s82iqpEORLx5XZ7YLgJGHdal7NXbWPfCwpSfqSGaiE8nBUZtALaqdzRlro q8UXWaP4A9bkQ== Message-ID: <848cbe1c-d84d-4377-8709-bb98d1d83146@kernel.org> Date: Mon, 2 Dec 2024 07:12:11 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH tty-next v3 1/6] serial: 8250: Adjust the timeout for FIFO mode To: John Ogness , "Maciej W. Rozycki" Cc: Greg Kroah-Hartman , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , Esben Haabendal , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Andy Shevchenko , Rengarajan S , Jeff Johnson , Serge Semin , Lino Sanfilippo , Wander Lairson Costa References: <20241025105728.602310-1-john.ogness@linutronix.de> <20241025105728.602310-2-john.ogness@linutronix.de> <837a7ecd-be29-4865-9543-cb6f7e7e46e7@kernel.org> <2fab2ef8-d0d6-4b94-90b6-7c16641a2f68@kernel.org> <84ldxzccjl.fsf@jogness.linutronix.de> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; keydata= xsFNBE6S54YBEACzzjLwDUbU5elY4GTg/NdotjA0jyyJtYI86wdKraekbNE0bC4zV+ryvH4j rrcDwGs6tFVrAHvdHeIdI07s1iIx5R/ndcHwt4fvI8CL5PzPmn5J+h0WERR5rFprRh6axhOk rSD5CwQl19fm4AJCS6A9GJtOoiLpWn2/IbogPc71jQVrupZYYx51rAaHZ0D2KYK/uhfc6neJ i0WqPlbtIlIrpvWxckucNu6ZwXjFY0f3qIRg3Vqh5QxPkojGsq9tXVFVLEkSVz6FoqCHrUTx wr+aw6qqQVgvT/McQtsI0S66uIkQjzPUrgAEtWUv76rM4ekqL9stHyvTGw0Fjsualwb0Gwdx ReTZzMgheAyoy/umIOKrSEpWouVoBt5FFSZUyjuDdlPPYyPav+hpI6ggmCTld3u2hyiHji2H cDpcLM2LMhlHBipu80s9anNeZhCANDhbC5E+NZmuwgzHBcan8WC7xsPXPaiZSIm7TKaVoOcL 9tE5aN3jQmIlrT7ZUX52Ff/hSdx/JKDP3YMNtt4B0cH6ejIjtqTd+Ge8sSttsnNM0CQUkXps w98jwz+Lxw/bKMr3NSnnFpUZaxwji3BC9vYyxKMAwNelBCHEgS/OAa3EJoTfuYOK6wT6nadm YqYjwYbZE5V/SwzMbpWu7Jwlvuwyfo5mh7w5iMfnZE+vHFwp/wARAQABzSFKaXJpIFNsYWJ5 IDxqaXJpc2xhYnlAa2VybmVsLm9yZz7CwXcEEwEIACEFAlW3RUwCGwMFCwkIBwIGFQgJCgsC BBYCAwECHgECF4AACgkQvSWxBAa0cEnVTg//TQpdIAr8Tn0VAeUjdVIH9XCFw+cPSU+zMSCH eCZoA/N6gitEcnvHoFVVM7b3hK2HgoFUNbmYC0RdcSc80pOF5gCnACSP9XWHGWzeKCARRcQR 4s5YD8I4VV5hqXcKo2DFAtIOVbHDW+0okOzcecdasCakUTr7s2fXz97uuoc2gIBB7bmHUGAH XQXHvdnCLjDjR+eJN+zrtbqZKYSfj89s/ZHn5Slug6w8qOPT1sVNGG+eWPlc5s7XYhT9z66E l5C0rG35JE4PhC+tl7BaE5IwjJlBMHf/cMJxNHAYoQ1hWQCKOfMDQ6bsEr++kGUCbHkrEFwD UVA72iLnnnlZCMevwE4hc0zVhseWhPc/KMYObU1sDGqaCesRLkE3tiE7X2cikmj/qH0CoMWe gjnwnQ2qVJcaPSzJ4QITvchEQ+tbuVAyvn9H+9MkdT7b7b2OaqYsUP8rn/2k1Td5zknUz7iF oJ0Z9wPTl6tDfF8phaMIPISYrhceVOIoL+rWfaikhBulZTIT5ihieY9nQOw6vhOfWkYvv0Dl o4GRnb2ybPQpfEs7WtetOsUgiUbfljTgILFw3CsPW8JESOGQc0Pv8ieznIighqPPFz9g+zSu Ss/rpcsqag5n9rQp/H3WW5zKUpeYcKGaPDp/vSUovMcjp8USIhzBBrmI7UWAtuedG9prjqfO wU0ETpLnhgEQAM+cDWLL+Wvc9cLhA2OXZ/gMmu7NbYKjfth1UyOuBd5emIO+d4RfFM02XFTI t4MxwhAryhsKQQcA4iQNldkbyeviYrPKWjLTjRXT5cD2lpWzr+Jx7mX7InV5JOz1Qq+P+nJW YIBjUKhI03ux89p58CYil24Zpyn2F5cX7U+inY8lJIBwLPBnc9Z0An/DVnUOD+0wIcYVnZAK DiIXODkGqTg3fhZwbbi+KAhtHPFM2fGw2VTUf62IHzV+eBSnamzPOBc1XsJYKRo3FHNeLuS8 f4wUe7bWb9O66PPFK/RkeqNX6akkFBf9VfrZ1rTEKAyJ2uqf1EI1olYnENk4+00IBa+BavGQ 8UW9dGW3nbPrfuOV5UUvbnsSQwj67pSdrBQqilr5N/5H9z7VCDQ0dhuJNtvDSlTf2iUFBqgk 3smln31PUYiVPrMP0V4ja0i9qtO/TB01rTfTyXTRtqz53qO5dGsYiliJO5aUmh8swVpotgK4 /57h3zGsaXO9PGgnnAdqeKVITaFTLY1ISg+Ptb4KoliiOjrBMmQUSJVtkUXMrCMCeuPDGHo7 39Xc75lcHlGuM3yEB//htKjyprbLeLf1y4xPyTeeF5zg/0ztRZNKZicgEmxyUNBHHnBKHQxz 1j+mzH0HjZZtXjGu2KLJ18G07q0fpz2ZPk2D53Ww39VNI/J9ABEBAAHCwV8EGAECAAkFAk6S 54YCGwwACgkQvSWxBAa0cEk3tRAAgO+DFpbyIa4RlnfpcW17AfnpZi9VR5+zr496n2jH/1ld wRO/S+QNSA8qdABqMb9WI4BNaoANgcg0AS429Mq0taaWKkAjkkGAT7mD1Q5PiLr06Y/+Kzdr 90eUVneqM2TUQQbK+Kh7JwmGVrRGNqQrDk+gRNvKnGwFNeTkTKtJ0P8jYd7P1gZb9Fwj9YLx jhn/sVIhNmEBLBoI7PL+9fbILqJPHgAwW35rpnq4f/EYTykbk1sa13Tav6btJ+4QOgbcezWI wZ5w/JVfEJW9JXp3BFAVzRQ5nVrrLDAJZ8Y5ioWcm99JtSIIxXxt9FJaGc1Bgsi5K/+dyTKL wLMJgiBzbVx8G+fCJJ9YtlNOPWhbKPlrQ8+AY52Aagi9WNhe6XfJdh5g6ptiOILm330mkR4g W6nEgZVyIyTq3ekOuruftWL99qpP5zi+eNrMmLRQx9iecDNgFr342R9bTDlb1TLuRb+/tJ98 f/bIWIr0cqQmqQ33FgRhrG1+Xml6UXyJ2jExmlO8JljuOGeXYh6ZkIEyzqzffzBLXZCujlYQ DFXpyMNVJ2ZwPmX2mWEoYuaBU0JN7wM+/zWgOf2zRwhEuD3A2cO2PxoiIfyUEfB9SSmffaK/ S4xXoB6wvGENZ85Hg37C7WDNdaAt6Xh2uQIly5grkgvWppkNy4ZHxE+jeNsU7tg= In-Reply-To: <84ldxzccjl.fsf@jogness.linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 04. 11. 24, 15:13, John Ogness wrote: > On 2024-11-04, Jiri Slaby wrote: >> Instead of looping fifosize multiplied by random timeout, can we >> re-use port->frame_time? > > Rather than 10k loops, we could loop > > (port->frame_time * some_scaled_padding) / 1000 > > times. The padding is important because we should not timeout in the > normal scenario. Perhaps using ~2 as @some_padding. Something like: > > port->frame_time >> 9 > > ? No, spell it out as you did above: port->frame_time * 2 / NSEC_PER_USEC >>> The difference between THRE and TEMT is the state of the shift register >>> only[2]: >>> >>> "In the FIFO mode, TEMT is set when the transmitter FIFO and shift >>> register are both empty." >> >> But what's the purpose of spinning _here_? The kernel can run and >> FIFO too. Without the kernel waiting for the FIFO. >> >> If we want to wait for fifo to empty, why not *also* the TSR. Meaning: >> >> Did you want UART_LSR_TEMT? > > Let us assume we have a line with 640 characters and a FIFO of 64 > bytes. For this line, we must wait for the FIFO to empty 10 times. It is > enough to wait for THRE for each of the 64-byte blocks because we are > only interested in refilling the FIFO at this point. Only at the very > end (in the caller... serial8250_console_write()) do we need to wait > for everything to flush to the wire (TEMT). > > By waiting on TEMT for each of the 64-byte blocks, we are waiting longer > than necessary. This creates a small window where the FIFO is empty and > there is nothing being transmitted. > > I did a simple test on my beaglebone-black hardware, sending 100 lines > of 924 bytes at 9600 bps. Since my hardware uses a 64-byte FIFO, each > line would have 14 such windows. > > And indeed, waiting for TEMT rather than only THRE for the 64-byte > blocks resulted in an extra 30ms total transfer for all 92400 > bytes. That is about 20us lost in each window by unnecessarily waiting > for TEMT. Sure -- you still misunderstand me. I am still asking why do you want to wait for the TX machinery at the *end* (for the last 64 B of the 640 B line) of transmission at all? It occurs to me as wasted cycles. thanks, -- js suse labs