netdev - Re: [PATCH 2/2] net: dummy: allocate devices with alloc_netdev

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Message-ID: <BANLkTi=8mHr=SaUacW5cFR5xqXPaxrg5Xw@mail.gmail.com>
Date:	Tue, 7 Jun 2011 10:49:12 +0300
From:	Lucian Adrian Grijincu <lucian.grijincu@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 2/2] net: dummy: allocate devices with alloc_netdev_id

On Tue, Jun 7, 2011 at 6:19 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mardi 07 juin 2011 à 04:39 +0300, Lucian Adrian Grijincu a écrit :
>> The most like case is that no one else is registering devices with a
>> name like "dummy%d".
>>
>> We can bring the complexity down by replacing:
>> - alloc_netdev_id which is O(N) with
>> - alloc_netdev_id which, on the average case, is O(1).
>>
>> $ time modprobe dummy numdummies=5000
>> - with alloc_netdev   : 9.50s
>> - with alloc_netdev_id: 3.50s
>>
>> NOTE: Stats generated on a heavily patched 3.0-rc1 which replaces the
>>       current O(N^2) sysctl algorithm with a better one.
>
> Yes, and disabled hotplug I guess.

$ cat .config | grep HOTPLUG
CONFIG_HOTPLUG=y
# CONFIG_MEMORY_HOTPLUG is not set
CONFIG_HOTPLUG_CPU=y
CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y
CONFIG_ACPI_HOTPLUG_CPU=y
# CONFIG_HOTPLUG_PCI is not set

I would guess you're going for CONFIG_HOTPLUG_PCI or
CONFIG_HOTPLUG_CPU, but I don't understand the implications.

> Dont try this on a random computer ;)

Could you briefly explain what's at stake here? What can go wrong if
we do this? I wasn't advocating replacing all alloc_netdev calls with
the new call.

> # time modprobe dummy numdummies=5000
>
> real    4m45.646s
> user    0m0.000s
> sys     0m12.440s
> # uptime
>  05:13:46 up 13:30,  3 users,  load average: 11221.41, 6918.70, 3101.12
> # uptime
>  05:18:45 up 13:35,  3 users,  load average: 12159.82, 10277.39, 5623.19

I don't get where you're going with these stats.

I don't care much about these patches, and even less if they're
fundamentally borked, but I'd like to know how/why they're not ok.

Please spare a second and illuminate me; I feel left out on a big joke.

-- 
 .
..: Lucian
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