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([2001:a61:1335:3601:f121:69fe:935a:67bd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-442cd3b7e26sm201015165e9.37.2025.05.13.01.21.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 May 2025 01:21:07 -0700 (PDT) Message-ID: <875848ec-f92b-48a9-b5c2-792bb0121824@suse.com> Date: Tue, 13 May 2025 10:21:06 +0200 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 2/2] USB: xhci: use urb hcpriv mempool for private data To: David Wang <00107082@163.com>, mathias.nyman@intel.com, gregkh@linuxfoundation.org Cc: stern@rowland.harvard.edu, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250512150724.4560-1-00107082@163.com> <20250513055545.5738-1-00107082@163.com> Content-Language: en-US From: Oliver Neukum In-Reply-To: <20250513055545.5738-1-00107082@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 13.05.25 07:55, David Wang wrote: > xhci keeps alloc/free private data for each enqueue/dequeue cycles, > when using a USB webcam, the memory allocation frequency could reach > about 1k/s. > > URB objects have longer lifecycle than private data, hand over ownership > of private data to urb can save lots of memory allocations over time. I am afraid I need to make a comment about a principal issue. This patch set overlooks a fundamental issue. You cannot guarantee that an URB is reused by the same HC. For example you cannot rule out that the next time your URB is resubmitted, it will land with XHCI again. That means you cannot touch just how one HCD handles private data. Or you need to record which HC the URB was last used for. Regards Oliver