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[dm-devel] Re: [PATCH 02/24] io-controller: Core of the elevator fair queuing



On Thu, Aug 20, 2009 at 04:51:46PM +0200, Jerome Marchand wrote:
> Vivek Goyal wrote:
> > On Wed, Aug 19, 2009 at 06:01:34PM +0200, Jerome Marchand wrote:
> >> Hi Vivek,
> >>
> >> Vivek Goyal wrote:
> >>> o This is core of the io scheduler implemented at elevator layer. This is a mix
> >>>   of cpu CFS scheduler and CFQ IO scheduler. Some of the bits from CFS have
> >>>   to be derived so that we can support hierarchical scheduling. Without
> >>>   cgroups or with-in group, we should essentially get same behavior as CFQ.
> >>>
> >>> o This patch only shows non-hierarchical bits. Hierarhical code comes in later
> >>>   patches.
> >>>
> >>> o This code is the building base of introducing fair queuing logic in common
> >>>   elevator layer so that it can be used by all the four IO schedulers.
> >>> +static void enqueue_io_entity(struct io_entity *entity)
> >>> +{
> >>> +	struct io_service_tree *st = entity->st;
> >>> +	struct io_sched_data *sd = io_entity_sched_data(entity);
> >>> +
> >>> +	/* In case task ioprio class changed while entity was off tree */
> >>> +	io_entity_update_prio(entity);
> >>> +	st->nr_active++;
> >>> +	sd->nr_active++;
> >>> +	entity->on_st = 1;
> >>> +	place_entity(st, entity, 0);
> >>> +	__enqueue_io_entity(st, entity);
> >>> +}
> 
> One more thing. io_entity_update_prio(entity) can change entity->st, so we'd
> better set st after io_entity_update_prio() call. I think it fixes a bug I've
> seen when changing elevator and ioprio_class at the same time:

Makes sense. I got three service trees and if a user has changed the
ioprio class it will also change the service tree on which entity should
go in. Hence "st" should be initialized only when we have accomodated the
prio class changes which ascertains the service tree also.

Thanks Jerome. Will merge it in next posting.

Vivek

> 
> ------------[ cut here ]------------
> kernel BUG at block/elevator-fq.c:1921!
> invalid opcode: 0000 [#1] SMP
> last sysfs file: /sys/block/sda/queue/scheduler
> Modules linked in: ipt_REJECT xt_tcpudp iptable_filter ip_tables x_tables bridge stp ipv6 autofs4 hidp rfcomm l2cap bluetooth rfkill sunrpc dm_mirror dm_region_hash dm_log dm_multipath scsi_dh dm_mod video output sbs sbshc battery ac netconsole lp snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device sg snd_pcm_oss snd_mixer_oss rtc_cmos sr_mod snd_pcm cdrom rtc_core tg3 snd_timer libphy snd serio_raw dcdbas i2c_i801 soundcore button pcspkr rtc_lib snd_page_alloc i2c_core parport_pc parport ata_piix libatasd_mod scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode]
> 
> Pid: 9127, comm: change_elevator Tainted: G   M       (2.6.31-rc6-io-controller-v8 #69) OptiPlex 745
> EIP: 0060:[<c0537867>] EFLAGS: 00010286 CPU: 1
> EIP is at elv_put_iog+0x61/0x83
> EAX: 00000000 EBX: 00000000 ECX: f607c000 EDX: f607c001
> ESI: f725d300 EDI: f3b59ee0 EBP: f60e5ec0 ESP: f60e5ebc
>  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> Process change_elevator (pid: 9127, ti=f60e5000 task=f38083f0 task.ti=f60e5000)
> Stack:
>  f607c000 f60e5ee8 c05382f5 f70ab480 f6abb368 00000086 f70ab480 00000000
> <0> f725d300 f725d334 f38d3cc0 f60e5ef8 c05248f7 f725d30c f6abb368 f60e5f28
> <0> c0524a67 00000005 00000000 f725d300 706f6f6e c0820000 f60e5f28 c069e51b
> Call Trace:
>  [<c05382f5>] ? elv_exit_fq_data+0x18d/0x195
>  [<c05248f7>] ? elevator_exit+0x28/0x4e
>  [<c0524a67>] ? elv_iosched_store+0x14a/0x1db
>  [<c069e51b>] ? mutex_lock_nested+0x2e/0x36
>  [<c052d1f8>] ? queue_attr_store+0x50/0x61
>  [<c04e9f56>] ? sysfs_write_file+0xb9/0xe4
>  [<c04e9e9d>] ? sysfs_write_file+0x0/0xe4
>  [<c04a9e57>] ? vfs_write+0x84/0xdf
>  [<c04a9f4b>] ? sys_write+0x3b/0x60
>  [<c04029b4>] ? sysenter_do_call+0x12/0x32
> Code: 0b eb fe 83 79 48 00 75 18 83 79 4c 00 75 1c 83 79 60 00 75 0c 83 79 64 00 75 10 83 79 78 00 74 04 0f 0b eb fe 83 79 7c 00 74 04 <0f> 0b eb fe 8d 81 ec 00 00 00 ba f6 65 53 c0 e8 e9 41 f3 ff 85
> EIP: [<c0537867>] elv_put_iog+0x61/0x83 SS:ESP 0068:f60e5ebc
> ---[ end trace f56eaa89c47eb665 ]---
> 
> With the following patch, I can't reproduce it anymore.
> 
> Regards,
> Jerome
> 
> Signed-off-by: Jerome Marchand <jmarchan redhat com>
> ---
>  elevator-fq.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> --- block/elevator-fq.c.orig	2009-08-20 16:39:13.000000000 +0200
> +++ block/elevator-fq.c	2009-08-20 14:29:04.000000000 +0200
> @@ -519,11 +519,12 @@ __enqueue_io_entity(struct io_service_tr
>  
>  static void enqueue_io_entity(struct io_entity *entity)
>  {
> -	struct io_service_tree *st = entity->st;
> +	struct io_service_tree *st;
>  	struct io_sched_data *sd = io_entity_sched_data(entity);
>  
>  	/* In case task ioprio class changed while entity was off tree */
>  	io_entity_update_prio(entity);
> +	st = entity->st;
>  	st->nr_active++;
>  	sd->nr_active++;
>  	entity->on_st = 1;


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