linux-kernel - Re: [PATCH 2/5] vmbus: suppress uevents for hv

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Message-ID: <20170910080944.GB3573@kroah.com>
Date:   Sun, 10 Sep 2017 10:09:44 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     kys@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        olaf@...fle.de, apw@...onical.com, vkuznets@...hat.com,
        jasowang@...hat.com, leann.ogasawara@...onical.com,
        marcelo.cerri@...onical.com, sthemmin@...rosoft.com,
        Dexuan Cui <decui@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [PATCH 2/5] vmbus: suppress uevents for hv_sock devices

On Sat, Sep 09, 2017 at 11:08:46PM -0700, kys@...hange.microsoft.com wrote:
> From: Dexuan Cui <decui@...rosoft.com>
> 
> hv_sock driver is automatically loaded when an application creates an
> AF_VSOCK socket, so we don't really need to trigger uevents to the user
> space udevd.
> 
> And hv_sock devices can appear and disappear frequency, e.g. 100 per
> second, so triggering the udevents can cause a high cpu utilization of
> udevd, e.g. 30% on a 2-cpu virtual machine. So let's suppress the
> uevents to avoid this.

100 per second for a struct device?  That's crazy, and the uevent is the
least of your worries.  Please fix that, as it's not the correct way to
use the driver model at all.

And really, why is uevent taking all that much cpu time anyway?  It
_should_ be pretty fast, unless your distro is doing crazy things with
it...

sorry, am not going to take this patch.

greg k-h