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
