[PATCH 1/2] hvc_console polling mode timer backoff

[PATCH 1/2] hvc_console polling mode timer backoff

[Will Schmidt]

Paulus, I think this is ready to go, please apply, thanks. 



Add a back-off mechanism to hvc_console's polling logic.   This change
drops the timers/second ratio from ~90 to ~1/2 while the console is
idle.
This change is most noticeable when watching /proc/timer_stats output.

This only affects when the hvc_console is running in poll mode, i.e.
power4 and cell systems.

I've tested on Power4, Michael Ellerman has both contributed to the
patch and tested on cell.   

Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
cc: Michael Ellerman <michael@ellerman.id.au>


---
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index a0a88aa..fc9bc77 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -47,8 +47,6 @@ #include "hvc_console.h"
 #define HVC_MAJOR	229
 #define HVC_MINOR	0
 
-#define TIMEOUT		(10)
-
 /*
  * Wait this long per iteration while trying to push buffered data to the
  * hypervisor before allowing the tty to complete a close operation.
@@ -550,6 +548,18 @@ static int hvc_chars_in_buffer(struct tt
 	return hp->n_outbuf;
 }
 
+/*
+ * timeout will vary between the MIN and MAX values defined here.  By default
+ * and during console activity we will use a default MIN_TIMEOUT of 10.  When
+ * the console is idle, we increase the timeout value on each pass through
+ * msleep until we reach the max.  This may be noticeable as a brief (average
+ * one second) delay on the console before the console responds to input when
+ * there has been no input for some time.
+ */
+#define MIN_TIMEOUT		(10)
+#define MAX_TIMEOUT		(2000)
+static u32 timeout = MIN_TIMEOUT;
+
 #define HVC_POLL_READ	0x00000001
 #define HVC_POLL_WRITE	0x00000002
 
@@ -642,9 +652,14 @@ #endif /* CONFIG_MAGIC_SYSRQ */
  bail:
 	spin_unlock_irqrestore(&hp->lock, flags);
 
-	if (read_total)
+	if (read_total) {
+		/* Activity is occurring, so reset the polling backoff value to
+		   a minimum for performance. */
+		timeout = MIN_TIMEOUT;
+
 		tty_flip_buffer_push(tty);
-	
+	}
+
 	return poll_mask;
 }
 
@@ -688,8 +703,12 @@ int khvcd(void *unused)
 		if (!hvc_kicked) {
 			if (poll_mask == 0)
 				schedule();
-			else
-				msleep_interruptible(TIMEOUT);
+			else {
+				if (timeout < MAX_TIMEOUT)
+					timeout += (timeout >> 6) + 1;
+
+				msleep_interruptible(timeout);
+			}
 		}
 		__set_current_state(TASK_RUNNING);
 	} while (!kthread_should_stop());

[PATCH 2/2] hvc_console typo fixes

[Will Schmidt]

Fix a handful of comment typos for hvc_console.


Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>

---

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index fc9bc77..0f9ed7b 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -102,12 +102,12 @@ static DEFINE_SPINLOCK(hvc_structs_lock)
 /*
  * This value is used to assign a tty->index value to a hvc_struct based
  * upon order of exposure via hvc_probe(), when we can not match it to
- * a console canidate registered with hvc_instantiate().
+ * a console candidate registered with hvc_instantiate().
  */
 static int last_hvc = -1;
 
 /*
- * Do not call this function with either the hvc_strucst_lock or the hvc_struct
+ * Do not call this function with either the hvc_structs_lock or the hvc_struct
  * lock held.  If successful, this function increments the kobject reference
  * count against the target hvc_struct so it should be released when finished.
  */
@@ -160,7 +160,7 @@ void hvc_console_print(struct console *c
 	if (index >= MAX_NR_HVC_CONSOLES)
 		return;
 
-	/* This console adapter was removed so it is not useable. */
+	/* This console adapter was removed so it is not usable. */
 	if (vtermnos[index] < 0)
 		return;
 
@@ -218,7 +218,7 @@ struct console hvc_con_driver = {
 };
 
 /*
- * Early console initialization.  Preceeds driver initialization.
+ * Early console initialization.  Precedes driver initialization.
  *
  * (1) we are first, and the user specified another driver
  * -- index will remain -1
@@ -255,7 +255,7 @@ int hvc_instantiate(uint32_t vtermno, in
 	if (vtermnos[index] != -1)
 		return -1;
 
-	/* make sure no no tty has been registerd in this index */
+	/* make sure no no tty has been registered in this index */
 	hp = hvc_get_by_index(index);
 	if (hp) {
 		kobject_put(&hp->kobj);
@@ -265,7 +265,7 @@ int hvc_instantiate(uint32_t vtermno, in
 	vtermnos[index] = vtermno;
 	cons_ops[index] = ops;
 
-	/* reserve all indices upto and including this index */
+	/* reserve all indices up to and including this index */
 	if (last_hvc < index)
 		last_hvc = index;
 
@@ -526,7 +526,7 @@ static int hvc_write(struct tty_struct *
 
 /*
  * This is actually a contract between the driver and the tty layer outlining
- * how much write room the driver can guarentee will be sent OR BUFFERED.  This
+ * how much write room the driver can guarantee will be sent OR BUFFERED.  This
  * driver MUST honor the return value.
  */
 static int hvc_write_room(struct tty_struct *tty)
@@ -813,7 +813,7 @@ int __devexit hvc_remove(struct hvc_stru
 
 	/*
 	 * We 'put' the instance that was grabbed when the kobject instance
-	 * was intialized using kobject_init().  Let the last holder of this
+	 * was initialized using kobject_init().  Let the last holder of this
 	 * kobject cause it to be removed, which will probably be the tty_hangup
 	 * below.
 	 */
@@ -869,7 +869,7 @@ int __init hvc_init(void)
 }
 module_init(hvc_init);
 
-/* This isn't particularily necessary due to this being a console driver
+/* This isn't particularly necessary due to this being a console driver
  * but it is nice to be thorough.
  */
 static void __exit hvc_exit(void)

Re: [PATCH 1/2] hvc_console polling mode timer backoff

[Michael Ellerman]

[-- Attachment #1: Type: text/plain, Size: 3068 bytes --]

On Tue, 2007-04-17 at 09:44 -0500, Will Schmidt wrote:
> Paulus, I think this is ready to go, please apply, thanks. 
> 
> 
> 
> Add a back-off mechanism to hvc_console's polling logic.   This change
> drops the timers/second ratio from ~90 to ~1/2 while the console is
> idle.
> This change is most noticeable when watching /proc/timer_stats output.
> 
> This only affects when the hvc_console is running in poll mode, i.e.
> power4 and cell systems.
> 
> I've tested on Power4, Michael Ellerman has both contributed to the
> patch and tested on cell.   
> 
> Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
> cc: Michael Ellerman <michael@ellerman.id.au>

That should probably be:

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>

cheers

> ---
> diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
> index a0a88aa..fc9bc77 100644
> --- a/drivers/char/hvc_console.c
> +++ b/drivers/char/hvc_console.c
> @@ -47,8 +47,6 @@ #include "hvc_console.h"
>  #define HVC_MAJOR	229
>  #define HVC_MINOR	0
>  
> -#define TIMEOUT		(10)
> -
>  /*
>   * Wait this long per iteration while trying to push buffered data to the
>   * hypervisor before allowing the tty to complete a close operation.
> @@ -550,6 +548,18 @@ static int hvc_chars_in_buffer(struct tt
>  	return hp->n_outbuf;
>  }
>  
> +/*
> + * timeout will vary between the MIN and MAX values defined here.  By default
> + * and during console activity we will use a default MIN_TIMEOUT of 10.  When
> + * the console is idle, we increase the timeout value on each pass through
> + * msleep until we reach the max.  This may be noticeable as a brief (average
> + * one second) delay on the console before the console responds to input when
> + * there has been no input for some time.
> + */
> +#define MIN_TIMEOUT		(10)
> +#define MAX_TIMEOUT		(2000)
> +static u32 timeout = MIN_TIMEOUT;
> +
>  #define HVC_POLL_READ	0x00000001
>  #define HVC_POLL_WRITE	0x00000002
>  
> @@ -642,9 +652,14 @@ #endif /* CONFIG_MAGIC_SYSRQ */
>   bail:
>  	spin_unlock_irqrestore(&hp->lock, flags);
>  
> -	if (read_total)
> +	if (read_total) {
> +		/* Activity is occurring, so reset the polling backoff value to
> +		   a minimum for performance. */
> +		timeout = MIN_TIMEOUT;
> +
>  		tty_flip_buffer_push(tty);
> -	
> +	}
> +
>  	return poll_mask;
>  }
>  
> @@ -688,8 +703,12 @@ int khvcd(void *unused)
>  		if (!hvc_kicked) {
>  			if (poll_mask == 0)
>  				schedule();
> -			else
> -				msleep_interruptible(TIMEOUT);
> +			else {
> +				if (timeout < MAX_TIMEOUT)
> +					timeout += (timeout >> 6) + 1;
> +
> +				msleep_interruptible(timeout);
> +			}
>  		}
>  		__set_current_state(TASK_RUNNING);
>  	} while (!kthread_should_stop());
> 
> 
> 
> 
-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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Re: [PATCH 1/2] hvc_console polling mode timer backoff

[Linas Vepstas]

On Tue, Apr 17, 2007 at 09:44:46AM -0500, Will Schmidt wrote:
> 
> Add a back-off mechanism to hvc_console's polling logic.   This change

Acked-by: Linas Vepstas <linas@austin.ibm.com>

--linas