From: Lennart Poettering <mzxreary@0pointer.de>
To: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>,
axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/17] blkcg: shoot down blkio_groups on elevator switch
Date: Mon, 23 Jan 2012 21:43:52 +0100 [thread overview]
Message-ID: <20120123204352.GB21822@tango.0pointer.de> (raw)
In-Reply-To: <20120123184336.GI12652@google.com>
On Mon, 23.01.12 10:43, Tejun Heo (tj@kernel.org) wrote:
>
> On Mon, Jan 23, 2012 at 01:27:45PM -0500, Vivek Goyal wrote:
> > > Why can't systemd order elevator switch before other actions?
> >
> > Because systemd does not know. For systemd it is just launching services
> > and what services are doing is not known to systemd.
> >
> > I think systemd does have some facilities so that services can express
> > dependency on other services and dependent service blocks on completion
> > of service it is depenent on. So may be in this case any service dealing
> > with cgroups shall have to be dependent on this service which tunes
> > the system and changes elevator.
>
> I'm sure systemd has enough facility for expressing this dependency.
> Where this configuration belongs to is a different question tho. I
> don't know how the tuned thing works but configurations like this are
> bound to devices and should be part of device discovery / hotplug
> sequence. IOW, it should be something which ultimately runs off udev
> events as part of device found event.
I didn't really follow the whole discussion here, but if this is about
adjusting parameters of a block device as the block device shows up this
must necessarily happen in an udev rule (and not in a daemon watching
block devices using libudev), since you most likely need the
synchronicity: i.e. you want to avoid that normal (libudev-using)
userspace code ever sees the device before those params are written to
the device. A daemon asynchronously watching the devices with libudev
for adjusting such tunables is necessarily racy.
Lennart
--
Lennart Poettering - Red Hat, Inc.
next prev parent reply other threads:[~2012-01-23 20:43 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-22 3:25 [PATCHSET] blkcg: kill policy node and blkg->dev, take#2 Tejun Heo
2012-01-22 3:25 ` [PATCH 01/17] blkcg: make CONFIG_BLK_CGROUP bool Tejun Heo
2012-01-23 15:00 ` Vivek Goyal
2012-01-23 15:34 ` Tejun Heo
2012-01-22 3:25 ` [PATCH 02/17] cfq: don't register propio policy if !CONFIG_CFQ_GROUP_IOSCHED Tejun Heo
2012-01-22 3:25 ` [PATCH 03/17] elevator: clear auxiliary data earlier during elevator switch Tejun Heo
2012-01-22 3:25 ` [PATCH 04/17] elevator: make elevator_init_fn() return 0/-errno Tejun Heo
2012-01-22 3:25 ` [PATCH 05/17] block: implement blk_queue_bypass_start/end() Tejun Heo
2012-01-22 3:25 ` [PATCH 06/17] block: extend queue bypassing to cover blkcg policies Tejun Heo
2012-01-22 3:25 ` [PATCH 07/17] blkcg: make blkio_list_lock irq-safe Tejun Heo
2012-01-22 3:25 ` [PATCH 08/17] blkcg: shoot down blkio_groups on elevator switch Tejun Heo
2012-01-23 15:20 ` Vivek Goyal
2012-01-23 15:36 ` Vivek Goyal
2012-01-23 15:49 ` Tejun Heo
2012-01-23 15:39 ` Tejun Heo
2012-01-23 15:52 ` Vivek Goyal
2012-01-23 15:57 ` Tejun Heo
2012-01-23 16:10 ` Vivek Goyal
2012-01-23 16:13 ` Vivek Goyal
2012-01-23 16:20 ` Tejun Heo
2012-01-23 16:28 ` Vivek Goyal
2012-01-23 16:32 ` Tejun Heo
2012-01-23 16:16 ` Tejun Heo
2012-01-23 16:25 ` Vivek Goyal
2012-01-23 17:10 ` Tejun Heo
2012-01-23 18:27 ` Vivek Goyal
2012-01-23 18:43 ` Tejun Heo
2012-01-23 19:33 ` Tejun Heo
2012-01-23 19:57 ` Vivek Goyal
2012-01-23 20:33 ` Tejun Heo
2012-01-23 20:43 ` Lennart Poettering [this message]
2012-01-23 20:47 ` Tejun Heo
2012-01-23 21:03 ` Vivek Goyal
2012-01-23 20:40 ` Lennart Poettering
2012-01-23 18:32 ` Vivek Goyal
2012-01-23 18:51 ` Tejun Heo
2012-01-22 3:25 ` [PATCH 09/17] blkcg: move rcu_read_lock() outside of blkio_group get functions Tejun Heo
2012-01-22 3:25 ` [PATCH 10/17] blkcg: update blkg get functions take blkio_cgroup as parameter Tejun Heo
2012-01-22 3:25 ` [PATCH 11/17] blkcg: use q and plid instead of opaque void * for blkio_group association Tejun Heo
2012-01-22 3:25 ` [PATCH 12/17] blkcg: add blkio_policy[] array and allow one policy per policy ID Tejun Heo
2012-01-22 3:25 ` [PATCH 13/17] blkcg: use the usual get blkg path for root blkio_group Tejun Heo
2012-01-22 3:25 ` [PATCH 14/17] blkcg: factor out blkio_group creation Tejun Heo
2012-01-22 3:25 ` [PATCH 15/17] blkcg: don't allow or retain configuration of missing devices Tejun Heo
2012-01-22 3:25 ` [PATCH 16/17] blkcg: kill blkio_policy_node Tejun Heo
2012-01-22 3:25 ` [PATCH 17/17] blkcg: kill the mind-bending blkg->dev Tejun Heo
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