Date:   Wed, 4 Apr 2018 11:57:19 +0200
From:   Paul Menzel <pmenzel+linux-ide@...gen.mpg.de>
To:     Hans de Goede <hdegoede@...hat.com>, Tejun Heo <tj@...nel.org>
Cc:     linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Decrease boot time with AHCI drives?

[Attach full output of `dmesg`.]

On 04/04/18 11:53, Paul Menzel wrote:
> Dear Linux folks,
> 
> 
> I am trying to decrease the boot time of the Linux kernel so the LUKS 
> passphrase dialog (in the initrd) is shown as quickly as possible. The 
> devices I test with is a Lenovo X60 and ASRock E350M1 both running with 
> coreboot and the GRUB payload. The goal is to do this without having to 
> rebuild a Linux kernel, but only by run-time
> 
> I am currently at 1.2 seconds.
> 
> ```
> [    0.610437] calling  ata_init+0x0/0x2be [libata] @ 88
> [    0.610548] libata version 3.00 loaded.
> [    0.610570] initcall ata_init+0x0/0x2be [libata] returned 0 after 107 
> usecs
> [    0.612100] calling  serio_raw_drv_init+0x0/0x1000 [serio_raw] @ 89
> [    0.612132] initcall serio_raw_drv_init+0x0/0x1000 [serio_raw] 
> returned 0 after 25 usecs
> [    0.612659] calling  ahci_pci_driver_init+0x0/0x1000 [ahci] @ 88
> [    0.612715] ahci 0000:00:1f.2: version 3.0
> [    0.613050] ahci 0000:00:1f.2: SSS flag set, parallel bus scan disabled
> [    0.613153] ahci 0000:00:1f.2: AHCI 0001.0100 32 slots 4 ports 1.5 
> Gbps 0x1 impl SATA mode
> [    0.613239] ahci 0000:00:1f.2: flags: 64bit ncq ilck stag pm led clo 
> pmp pio slum part
> [    0.613915] calling  evdev_init+0x0/0x1000 [evdev] @ 85
> [    0.614178] initcall evdev_init+0x0/0x1000 [evdev] returned 0 after 
> 250 usecs
> [    0.624366] scsi host0: ahci
> [    0.630638] scsi host1: ahci
> [    0.640413] scsi host2: ahci
> [    0.646559] scsi host3: ahci
> [    0.646752] ata1: SATA max UDMA/133 abar m1024@...4445000 port 
> 0xe4445100 irq 28
> [    0.646836] ata2: DUMMY
> [    0.646902] ata3: DUMMY
> [    0.646964] ata4: DUMMY
> [    0.647098] initcall ahci_pci_driver_init+0x0/0x1000 [ahci] returned 
> 0 after 33619 usecs
> [    1.124129] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
> [    1.124605] ata1.00: ATA-9: M4-CT256M4SSD2, 070H, max UDMA/100
> [    1.124674] ata1.00: 500118192 sectors, multi 16: LBA48 NCQ (depth 
> 31/32), AA
> [    1.125179] ata1.00: configured for UDMA/100
> [    1.125522] scsi 0:0:0:0: Direct-Access     ATA      M4-CT256M4SSD2 
> 070H PQ: 0 ANSI: 5
> [    1.129127] calling  init_sd+0x0/0x1000 [sd_mod] @ 84
> [    1.129268] initcall init_sd+0x0/0x1000 [sd_mod] returned 0 after 129 
> usecs
> [    1.129444] sd 0:0:0:0: [sda] 500118192 512-byte logical blocks: (256 
> GB/238 GiB)
> [    1.129550] sd 0:0:0:0: [sda] Write Protect is off
> [    1.129619] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
> [    1.129647] sd 0:0:0:0: [sda] Write cache: enabled, read cache: 
> enabled, doesn't support DPO or FUA
> [    1.130384]  sda: sda1 sda2
> [    1.131009] sd 0:0:0:0: [sda] Attached SCSI disk
> [    1.213492] calling  dm_init+0x0/0x31 [dm_mod] @ 110
> [    1.213535] device-mapper: uevent: version 1.0.3
> [    1.213727] device-mapper: ioctl: 4.37.0-ioctl (2017-09-20) 
> initialised: dm-devel@...hat.com
> [    1.213829] initcall dm_init+0x0/0x31 [dm_mod] returned 0 after 312 
> usecs
> [    1.214434] calling  dm_crypt_init+0x0/0x1000 [dm_crypt] @ 110
> [    1.214442] initcall dm_crypt_init+0x0/0x1000 [dm_crypt] returned 0 
> after 2 usecs
> ```
> 
> So, according to `initcall_debug` the method `ahci_pci_driver_init` 
> takes 33 ms to execute, which is longer then a few milliseconds.
> 
> But more importantly, it takes roughly half a second to set up the 
> device. I understand, that the probing is part of AHCI(?), and in this 
> case the Crucial m4 SSD drive/firmware is especially slow. So, I assume 
> it will be hard to improve anything in the code to decrease the time.
> 
> That said, in my case the assumption is, that the device configuration 
> will not change. That means, the drive will be the same and will be 
> connected to the same port all the time.
> 
> Additionally, GRUB already probed the device to read the Linux kernel 
> image and initrd image.
> 
> So, is there a way to avoid doing the probing twice or at all? That 
> means, either cache the settings, and load them during boot by reading 
> it from the firmware flash ROM chip, possible when using coreboot, and 
> passing it to the Linux kernel for example by GRUB. That would also help 
> with LinuxBoot [1], where the Linux kernel is used as the payload (boot 
> kernel), already setting up the drive and kexec’s another Linux kernel, 
> read from the drive.
> 
> Or, GRUB passes the settings it detected to the Linux kernel.
> 
> 
> Kind regards,
> 
> Paul
> 
> 
> [1] https://www.linuxboot.org/

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