Re: Regression in v5.0-rc1 with autosuspend hrtimers

[Vincent Guittot <vincent.guittot@linaro.org>]

On Wed, 9 Jan 2019 at 17:07, Ladislav Michl <ladis@linux-mips.org> wrote:
>
> On Wed, Jan 09, 2019 at 03:12:25PM +0100, Vincent Guittot wrote:
> > Please keep all thread list when replying :-)
>
> Ahh, sorry for that...
> [snip]
> > On Wed, 9 Jan 2019 at 14:33, Ladislav Michl <ladis@linux-mips.org> wrote:
> > > I agree, but it doea all the magic correctly, so you won't need
> > > to touch that code is ktime_t changes (I know, unlikely..)
> >
> > But the current implementation doesn't care of any changes in ktime_t
> > as it uses raw ns
>
> Fair enough, so let's go back to:

This one looks good for me

> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 70624695b6d5..e61ee9b47a26 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -121,7 +121,7 @@ static void pm_runtime_cancel_pending(struct device *dev)
>   * Compute the autosuspend-delay expiration time based on the device's
>   * power.last_busy time.  If the delay has already expired or is disabled
>   * (negative) or the power.use_autosuspend flag isn't set, return 0.
> - * Otherwise return the expiration time in jiffies (adjusted to be nonzero).
> + * Otherwise return the expiration time in nanoseconds (adjusted to be nonzero).
>   *
>   * This function may be called either with or without dev->power.lock held.
>   * Either way it can be racy, since power.last_busy may be updated at any time.
> @@ -129,24 +129,21 @@ static void pm_runtime_cancel_pending(struct device *dev)
>  u64 pm_runtime_autosuspend_expiration(struct device *dev)
>  {
>         int autosuspend_delay;
> -       u64 last_busy, expires = 0;
> -       u64 now = ktime_to_ns(ktime_get());
> +       u64 expires;
>
>         if (!dev->power.use_autosuspend)
> -               goto out;
> +               return 0;
>
>         autosuspend_delay = READ_ONCE(dev->power.autosuspend_delay);
>         if (autosuspend_delay < 0)
> -               goto out;
> -
> -       last_busy = READ_ONCE(dev->power.last_busy);
> +               return 0;
>
> -       expires = last_busy + autosuspend_delay * NSEC_PER_MSEC;
> -       if (expires <= now)
> -               expires = 0;    /* Already expired. */
> +       expires  = READ_ONCE(dev->power.last_busy);
> +       expires += NSEC_PER_MSEC * (u64)autosuspend_delay;
> +       if (expires > ktime_to_ns(ktime_get()))
> +               return expires; /* Expires in the future */
>
> - out:
> -       return expires;
> +       return 0;
>  }
>  EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
>
> Which gives for arm:
> 00000480 <pm_runtime_autosuspend_expiration>:
>      480:       e92d41f0        push    {r4, r5, r6, r7, r8, lr}
>      484:       e5d030d1        ldrb    r3, [r0, #209]  ; 0xd1
>      488:       e3130004        tst     r3, #4
>      48c:       0a00000c        beq     4c4 <pm_runtime_autosuspend_expiration+0x44>
>      490:       e59030e4        ldr     r3, [r0, #228]  ; 0xe4
>      494:       e3530000        cmp     r3, #0
>      498:       ba000009        blt     4c4 <pm_runtime_autosuspend_expiration+0x44>
>      49c:       e28050e8        add     r5, r0, #232    ; 0xe8
>      4a0:       e8950030        ldm     r5, {r4, r5}
>      4a4:       e59f2030        ldr     r2, [pc, #48]   ; 4dc <pm_runtime_autosuspend_expiration+0x5c>
>      4a8:       e0e54392        smlal   r4, r5, r2, r3
>      4ac:       ebfffffe        bl      0 <ktime_get>
>      4b0:       e1550001        cmp     r5, r1
>      4b4:       01540000        cmpeq   r4, r0
>      4b8:       e1a06004        mov     r6, r4
>      4bc:       e1a07005        mov     r7, r5
>      4c0:       8a000001        bhi     4cc <pm_runtime_autosuspend_expiration+0x4c>
>      4c4:       e3a06000        mov     r6, #0
>      4c8:       e3a07000        mov     r7, #0
>      4cc:       e1a00006        mov     r0, r6
>      4d0:       e1a01007        mov     r1, r7
>      4d4:       e8bd41f0        pop     {r4, r5, r6, r7, r8, lr}
>      4d8:       e12fff1e        bx      lr
>      4dc:       000f4240        .word   0x000f4240
>
> And x86:
> 0000000000000230 <pm_runtime_autosuspend_expiration.part.0>:
>      230:       8b 87 a4 01 00 00       mov    0x1a4(%rdi),%eax
>      236:       53                      push   %rbx
>      237:       85 c0                   test   %eax,%eax
>      239:       78 1e                   js     259 <pm_runtime_autosuspend_expiration.part.0+0x29>
>      23b:       48 63 d8                movslq %eax,%rbx
>      23e:       48 8b 97 a8 01 00 00    mov    0x1a8(%rdi),%rdx
>      245:       48 69 db 40 42 0f 00    imul   $0xf4240,%rbx,%rbx
>      24c:       48 01 d3                add    %rdx,%rbx
>      24f:       e8 00 00 00 00          callq  254 <pm_runtime_autosuspend_expiration.part.0+0x24>
>      254:       48 39 c3                cmp    %rax,%rbx
>      257:       77 02                   ja     25b <pm_runtime_autosuspend_expiration.part.0+0x2b>
>      259:       31 db                   xor    %ebx,%ebx
>      25b:       48 89 d8                mov    %rbx,%rax
>      25e:       5b                      pop    %rbx
>      25f:       c3                      retq
>
> 00000000000002a0 <pm_runtime_autosuspend_expiration>:
>      2a0:       f6 87 91 01 00 00 04    testb  $0x4,0x191(%rdi)
>      2a7:       74 02                   je     2ab <pm_runtime_autosuspend_expiration+0xb>
>      2a9:       eb 85                   jmp    230 <pm_runtime_autosuspend_expiration.part.0>
>      2ab:       31 c0                   xor    %eax,%eax
>      2ad:       c3                      retq
>      2ae:       66 90                   xchg   %ax,%ax
>
>
> [snip]
> > > Well, main concern was not to call ktime_get at the beginning of function
> > > as it is not too cheap.
> >
> > Doesn't the compiler optimize that to just before the test ?
>
> No (compare with above). And it is also almost certain that someone will run
> script and send "...do not needlesly initialize..." patch :)
>
> gcc version 8.2.1 20181130 (OSELAS.Toolchain-2018.12.0 8-20181130)
>
> 00000110 <pm_runtime_autosuspend_expiration>:
>      110:       e92d41f0        push    {r4, r5, r6, r7, r8, lr}
>      114:       e1a06000        mov     r6, r0
>      118:       ebfffffe        bl      0 <ktime_get>
>      11c:       e5d630d1        ldrb    r3, [r6, #209]  ; 0xd1
>      120:       e3130004        tst     r3, #4
>      124:       0a00000d        beq     160 <pm_runtime_autosuspend_expiration+0x50>
>      128:       e596c0e4        ldr     ip, [r6, #228]  ; 0xe4
>      12c:       e35c0000        cmp     ip, #0
>      130:       ba00000a        blt     160 <pm_runtime_autosuspend_expiration+0x50>
>      134:       e28630e8        add     r3, r6, #232    ; 0xe8
>      138:       e893000c        ldm     r3, {r2, r3}
>      13c:       e1a05001        mov     r5, r1
>      140:       e1a04000        mov     r4, r0
>      144:       e59f002c        ldr     r0, [pc, #44]   ; 178 <pm_runtime_autosuspend_expiration+0x68>
>      148:       e0010c90        mul     r1, r0, ip
>      14c:       e0926001        adds    r6, r2, r1
>      150:       e0a37fc1        adc     r7, r3, r1, asr #31
>      154:       e1550007        cmp     r5, r7
>      158:       01540006        cmpeq   r4, r6
>      15c:       3a000001        bcc     168 <pm_runtime_autosuspend_expiration+0x58>
>      160:       e3a06000        mov     r6, #0
>      164:       e3a07000        mov     r7, #0
>      168:       e1a00006        mov     r0, r6
>      16c:       e1a01007        mov     r1, r7
>      170:       e8bd41f0        pop     {r4, r5, r6, r7, r8, lr}
>      174:       e12fff1e        bx      lr
>      178:       000f4240        .word   0x000f4240