Re: [PATCH] ata,scsi: do not issue START STOP UNIT on resume

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Damien,

On Wed, Sep 13, 2023 at 12:21 PM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
> On Wed, Sep 13, 2023 at 12:58 AM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> > On 9/13/23 02:39, Geert Uytterhoeven wrote:
> > > On Mon, 31 Jul 2023, Damien Le Moal wrote:
> > >> During system resume, ata_port_pm_resume() triggers ata EH to
> > >> 1) Resume the controller
> > >> 2) Reset and rescan the ports
> > >> 3) Revalidate devices
> > >> This EH execution is started asynchronously from ata_port_pm_resume(),
> > >> which means that when sd_resume() is executed, none or only part of the
> > >> above processing may have been executed. However, sd_resume() issues a
> > >> START STOP UNIT to wake up the drive from sleep mode. This command is
> > >> translated to ATA with ata_scsi_start_stop_xlat() and issued to the
> > >> device. However, depending on the state of execution of the EH process
> > >> and revalidation triggerred by ata_port_pm_resume(), two things may
> > >> happen:
> > >> 1) The START STOP UNIT fails if it is received before the controller has
> > >>   been reenabled at the beginning of the EH execution. This is visible
> > >>   with error messages like:
> > >>
> > >> ata10.00: device reported invalid CHS sector 0
> > >> sd 9:0:0:0: [sdc] Start/Stop Unit failed: Result: hostbyte=DID_OK driverbyte=DRIVER_OK
> > >> sd 9:0:0:0: [sdc] Sense Key : Illegal Request [current]
> > >> sd 9:0:0:0: [sdc] Add. Sense: Unaligned write command
> > >> sd 9:0:0:0: PM: dpm_run_callback(): scsi_bus_resume+0x0/0x90 returns -5
> > >> sd 9:0:0:0: PM: failed to resume async: error -5
> > >>
> > >> 2) The START STOP UNIT command is received while the EH process is
> > >>   on-going, which mean that it is stopped and must wait for its
> > >>   completion, at which point the command is rather useless as the drive
> > >>   is already fully spun up already. This case results also in a
> > >>   significant delay in sd_resume() which is observable by users as
> > >>   the entire system resume completion is delayed.
> > >>
> > >> Given that ATA devices will be woken up by libata activity on resume,
> > >> sd_resume() has no need to issue a START STOP UNIT command, which solves
> > >> the above mentioned problems. Do not issue this command by introducing
> > >> the new scsi_device flag no_start_on_resume and setting this flag to 1
> > >> in ata_scsi_dev_config(). sd_resume() is modified to issue a START STOP
> > >> UNIT command only if this flag is not set.
> > >>
> > >> Reported-by: Paul Ausbeck <paula@xxxxxxxxxxxx>
> > >> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=215880
> > >> Fixes: a19a93e4c6a9 ("scsi: core: pm: Rely on the device driver core for async power management")
> > >> Signed-off-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
> > >
> > > Thanks for your patch, which is now commit 0a8589055936d8fe
> > > ("ata,scsi: do not issue START STOP UNIT on resume") in v6.5-rc5.
> > > Sorry for being late to the party, but this commit landed upstream
> > > during my summer holidays, and apparently I wasn't that focussed on
> > > noticing small behavioral changes after getting back to work...
> > >
> > > I noticed an oddity after s2idle or s2ram on Renesas Salvator-XS (R-Car
> > > H3 ES2.0) with an old (spinning rust) SATA drive, and bisected it to
> > > this commit: when accessing the drive after system resume, there is now
> > > a delay of ca. 5s before data is returned, presumably due to starting
> > > the drive, and having to wait for it to spin up to be able to read data.
> > > But the good news is that the actual system resume takes less time than
> > > before (reduced by even more than ca. 5s!), so this looks like a net
> > > win...
> >
> > Thanks for the report. The delay for the first data access from user space right
> > after resume is 100% expected, with or without this patch. The reason is that
> > waking up the drive (spinning it up) is done asynchronously from the PM resume
> > context, so when you get "PM suspend exit" message signaling that the system is
> > resumed, the drive may not yet be spinning. Any access will wait for that to
> > happen before proceeding. Depending on the drive that can take up to 10s or so.
>
> That does not match with what I am seeing: before this patch, there
> was no delay on first data access from user space, as the drive is fully
> spun up when system resume returns.
> With this patch, system resume returns earlier, and the drive is only
> spun up when user space starts accessing data.
>
> Note that I do not have any file system mounted, and use
> "hd /dev/sda | head -70" to access the disk.
>
> > I am not entirely sure where the net win you see come from. But the patch you
> > mention is in fact completely wrong and does not fix the underlying issues with
> > ata suspend/resume and potential deadlocks in PM due to ata ports relationship
> > with scsi devices. So I have been working on fixing this for the last 2 weeks,
> > after another user also reported issues with the patch you mention [1].
> >
> > Could you try libata for-next branch on your system ? There are 7 fix patches in
> > there that I plan to send out for 6.6-rc2 to fix the patch in question and other
> > issues potentially causing deadlocks on resume. The patches were posted also [2].
> >
> > https://lore.kernel.org/linux-ide/20230912005655.368075-1-dlemoal@xxxxxxxxxx/T/#t
>
> Unfortunately that didn't work, as /dev/sda no longer exists.
> Will reply to the patch I bisected the issue to...

With libata/for-next (fa2259a59966c005 ("ata: libata: Cleanup inline
DMA helper functions")) and commit 99626085d036ec32 ("ata: libata-scsi:
link ata port and scsi device") reverted, it behaves as before (disk
is spun up when system resume completes, no delay when accessing the
disk from userspace).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds



[Index of Archives]     [Linux Filesystems]     [Linux SCSI]     [Linux RAID]     [Git]     [Kernel Newbies]     [Linux Newbie]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Samba]     [Device Mapper]

  Powered by Linux