Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759480Ab3EWPVV (ORCPT ); Thu, 23 May 2013 11:21:21 -0400 Received: from mail-ie0-f169.google.com ([209.85.223.169]:44829 "EHLO mail-ie0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758873Ab3EWPVU (ORCPT ); Thu, 23 May 2013 11:21:20 -0400 MIME-Version: 1.0 In-Reply-To: References: <20130521230332.GC12713@redhat.com> <519D1668.6000601@zytor.com> <20130522200012.GA15456@redhat.com> <20130523033911.GA9411@redhat.com> Date: Thu, 23 May 2013 23:21:19 +0800 Message-ID: Subject: Re: microcode loading got really slow. From: Ming Lei To: Takashi Iwai Cc: Dave Jones , "H. Peter Anvin" , Linux Kernel , x86@kernel.org, fenghua.yu@intel.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5944 Lines: 145 On Thu, May 23, 2013 at 10:36 PM, Takashi Iwai wrote: > At Thu, 23 May 2013 22:28:51 +0800, > Ming Lei wrote: >> >> On Thu, May 23, 2013 at 9:21 PM, Takashi Iwai wrote: >> > At Thu, 23 May 2013 21:04:53 +0800, >> > Ming Lei wrote: >> >> >> >> On Thu, May 23, 2013 at 8:05 PM, Takashi Iwai wrote: >> >> > At Thu, 23 May 2013 18:45:29 +0800, >> >> > Ming Lei wrote: >> >> >> >> >> >> On Thu, May 23, 2013 at 6:36 PM, Takashi Iwai wrote: >> >> >> > >> >> >> > No, f/w loader always fall back to user mode helper, as long as its >> >> >> > support is built in. And doing that for microcode driver in that code >> >> >> > path isn't only superfluous but also broken due to request_firmware >> >> >> > call in module init. >> >> >> >> >> >> Firstly, it is not good to do this since some distributions doesn't support >> >> >> direct loading and doesn't have udevd(such as, android). >> >> >> >> >> >> Secondly, returning failure from request_firmware_direct() doesn't mean >> >> >> the firmware doesn't exist since distribution may put the firmware other where. >> >> > >> >> > Right, the non-standard path is the problem, and basically the only >> >> > problem. The distribution that doesn't support the direct loading >> >> > means nothing but that. >> >> >> >> Suppose it is, it is the fact, and it isn't OK to break this distribution. >> >> >> >> Also udev supports user-defined rules to load firmware, which >> >> means some drivers may not put their firmware in the default >> >> path of distribution's firmware. >> > >> > It's why I suggested to put a warning in that path as the first step. >> > So we can see whether there is any actual user. >> >> If you plan to do it, it'd better to add default firmware path of some >> distributions into firmware_class.c first, otherwise it may cause >> unnecessary noise for this distribution. >> >> But if more default search paths are added, it might cause mistaken >> firmwares found under incorrect path, for example, android's >> default path is "/etc/firmware" and "/vendor/firmware"(maybe different >> for different versions). >> >> Also, putting default search paths into kernel isn't good, which was >> introduced unwillingly for well-known reason. > > Maybe we can create a new Kconfig to specify non-standard firmware > path? Yes. > > >> >> >> Anyway, this example is very specific(no firmware can be accepted), and >> >> >> request_firmware_nowait() should be OK for the situation. >> >> > >> >> > Oh no, rewriting with request_firmware_nowait() should be really the >> >> > last choice. It would change the code flow awfully bad in most >> >> > cases. >> >> > >> >> > The new kernel driver has a better firmware mechanism. If it's only >> >> > the question of paths, we should move on toward that direction and >> >> > drop the too complex old way. I'd vote for a warning shown when a >> >> >> >> Simply dropping the old way may cause user space regression. >> > >> > It's already broken :) >> >> It is different, the current issue is caused by udev, not by kernel, :-) > > Yeah :) > > >> >> > firmware file is loaded via user mode helper (except for explicit >> >> > cases like FW_ACTION_NOHOTPLUG), for example. >> >> >> >> As it is a very driver specific problem, it is better to solve it inside driver. >> > >> > Yes, this proposal is basically not meant as a fix for this particular >> > issue but rather for future movement in general. >> > >> >> >> >> wrt. this problem, I think we >> >> >> >> need to know why the direct loading is failed. >> >> >> > >> >> >> > The reason is obvious: the requested f/w file doesn't exist. >> >> >> > And it's fine, because the microcode update is an optional operation. >> >> >> > If no f/w file is found, it's not handled as an error. It just means >> >> >> > that no need to update, continuing to work. >> >> >> >> >> >> OK, as said above, the example is very specific, and might be >> >> >> workarounded by request_firmware_nowait(). >> >> > >> >> > It's not that easy in this case. The microcode loader driver core >> >> > module doesn't invoke request_firmware() directly but it's via cpu >> >> > driver. And the same callback is called in different code paths, not >> >> > only at init but also via sysfs write. Thus the request_firmware() >> >> > call must be synchronous there. >> >> >> >> I don't think the way is too difficult to implement. In the path which >> >> requires synchronization, it can be waited on one completion after >> >> calling request_firmware_nowait(). >> > >> > This sounds already like unnecessary complexity. Also, what if >> > concurrent accesses? >> >> The request_firmware_no_wait() supports concurrent accesses on >> either same firmware or not. > > Yes, but I meant about the synchronization part. Then you'll need > multiple waiters. If request_firmware_no_wait() is called on one same firmware image, one waiter should be OK since the returned data is same for all requests. > >> > Also, I wonder why the kernel needs to be "fixed" for this, if the >> > problem is really the stuck in udev. In this regard, we didn't change >> > anything from the beginning. There was an implicit "wish", that the >> > f/w loading shouldn't be done in the module init, but this has been >> > never treated as a golden rule. >> >> No, there isn't the golden rule, and it is reasonable or inevitable >> sometimes to load firmware in module init, for example, I remember some >> wireless dongles in which people can't read its mac address without >> downloading firmware, that means some devices may not be initialized >> successfully without firmware. > > Right. > > > Takashi Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/