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

From: Vincent Guittot
Date: Wed Jan 09 2019 - 11:32:46 EST

On Wed, 9 Jan 2019 at 17:07, Ladislav Michl <ladis@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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