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 B183411CBA; Thu, 26 Jun 2025 00:00:51 +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=1750896051; cv=none; b=aupInaohlTRTIvmYEZjl8DTnM8KGcXtQQBTw5BPSrZ4N1Q8bUhQ1qj2CGtotITFVymwUvrj3vHeJIb//GYTjlhbM1SouG2lAJQrlacjP/pKq5/+CsPAZw+oGBUOa4OG2H4zEFYqVsMfwaz54F/EnBuUTO1bCoheKRFZiKmzHtAU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750896051; c=relaxed/simple; bh=tZ4wRwRuH0O3JH2xMlilUiVAzRnwvyZ54IObfur1zhU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OL4s6ksNkuzNxPIQ27QjtfgutmM6gE7Nm0rA/+CzdYn+98r9gQsjdWgP2s9yIQt3AbtCNvJJGS0+om7VQcyuU9Vg7cQejwYs2VZW/Fin1XJYTZDg/hEfBiGlXrmQRcH/GO+h7xBP6R9Dpnv+bIprPB5squCOuk+SESfUcBFup/A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SgkuH7YN; 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="SgkuH7YN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B1ABC4CEEA; Thu, 26 Jun 2025 00:00:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750896051; bh=tZ4wRwRuH0O3JH2xMlilUiVAzRnwvyZ54IObfur1zhU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SgkuH7YNryEma3tLhMxS3YDiei/raSSBQzeH1fvLyMSDqU8zOKAjc9f7CwYBKNOKP g6fhFbMAIUxitnD7jXAU8XmLW6N90G59dFRSZz9rIwdTnt+/4soU1mQDUBUyKcTdE5 2vDabNB8F7i8Qaz+WrPCS85rl9V4uAoH1SfHPH8uSRsl0qmRP19mU5oIYbE1Mrv9RP UvBaGaF00aO8/5PO+BHsNYeC1d8pUPIFn4bItIhyFmi39TViiBxzHJga7sKxqjjPvd yXD80YaaSk0oCFV5sIGiee2w0Cdnlf8ww7sI/jR7l5bLMNVwTSK/9SefBBITJG01/q A9nMfu0AvQvDQ== Message-ID: Date: Thu, 26 Jun 2025 09:00:49 +0900 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v18 02/12] block: Rework request allocation in blk_mq_submit_bio() To: Bart Van Assche , Jens Axboe Cc: linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, Christoph Hellwig References: <20250616223312.1607638-1-bvanassche@acm.org> <20250616223312.1607638-3-bvanassche@acm.org> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20250616223312.1607638-3-bvanassche@acm.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/17/25 07:33, Bart Van Assche wrote: > Prepare for allocating a request from a specific hctx by making > blk_mq_submit_bio() allocate a request later. > > The performance impact of this patch on the hot path is small: if a > request is cached, one percpu_ref_get(&q->q_usage_counter) call and one > percpu_ref_put(&q->q_usage_counter) call are added to the hot path. Numbers ? The change is forcing a queue enter for all BIOs because you remove the cached request optimization. So I am not sure it is the impact is that small if you have a very fast storage device. -- Damien Le Moal Western Digital Research