Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934587AbeAIRzW (ORCPT + 1 other); Tue, 9 Jan 2018 12:55:22 -0500 Received: from mail-io0-f170.google.com ([209.85.223.170]:46168 "EHLO mail-io0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752152AbeAIRzU (ORCPT ); Tue, 9 Jan 2018 12:55:20 -0500 X-Google-Smtp-Source: ACJfBou9HQeTMxFbw54zsax3nx6iW2pSaSo9nsuV/EIFlLHx3F+v/llGkDd2lg1/E0EyUBMSQHN2iU4K26AItXrbWQs= MIME-Version: 1.0 In-Reply-To: <20180109154235.2a42f0a0@vento.lan> References: <20180109154235.2a42f0a0@vento.lan> From: Linus Torvalds Date: Tue, 9 Jan 2018 09:55:18 -0800 X-Google-Sender-Auth: tnD7BM0cxrNoUcMqHp1DGnD0lzw Message-ID: Subject: Re: dvb usb issues since kernel 4.9 To: Mauro Carvalho Chehab Cc: Peter Zijlstra , Alan Stern , Ingo Molnar , Josef Griebichler , Greg Kroah-Hartman , USB list , Eric Dumazet , Rik van Riel , Paolo Abeni , Hannes Frederic Sowa , Jesper Dangaard Brouer , linux-kernel , netdev , Jonathan Corbet , LMML , David Miller Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Tue, Jan 9, 2018 at 9:42 AM, Mauro Carvalho Chehab wrote: > > On my preliminar tests, writing to a file on an ext4 partition at a > USB stick loses data up to the point to make it useless (1/4 of the data > is lost!). However, writing to a class 10 microSD card is doable. Note that most USB sticks are horrible crap. They can have write latencies counted in _seconds_. You can cause VM issues and various other non-hardware stalls with them, simply because something gets stuck waiting for a page writeout that should take a few ms on any reasonable hardware, but ends up talking half a second or more. For example, even really well-written software that tries to do things like threaded write-behind to smooth out the IO will be _totally_ screwed by the USB stick behavior (where you might write a few MB at high speeds, and then the next write - however small - takes a second because the stupid USB stick does a synchronous garbage collection. Suddenly all that clever software that tried to keep things moving along smoothly without any hiccups, and tried hard to make the USB bus have a nice constant loadm can't do anything at all about the crap hardware. So when testing writes to USB sticks, I'm not convinced you're actually testing any USB bus limitations or even really any other hardware limitations than the USB stick itself. Linus