spi: Add cond_resched() in main message processing loop

broonie · broonie · commit 628269704f19 · 2016-02-18T17:41:44.000Z
When a controller has only PIO support it is very likely that we will
run into use cases where we spend a very large amount of time consuming
CPU.  Code that does this should call cond_resched() every once in a
while to give other tasks more of a chance to run so do that in the main
SPI loop, the overhead is negligable if it's not needed.

Suggested-by: Arnd Bergmann &lt;arnd@arndb.de&gt;
Signed-off-by: Mark Brown &lt;broonie@kernel.org&gt;
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
@@ -1184,6 +1184,9 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
 		return;
 	}
 	mutex_unlock(&master->bus_lock_mutex);
+
+	/* Prod the scheduler in case transfer_one() was busy waiting */
+	cond_resched();
 }
 
 /**

Original file line number	Diff line number	Diff line change
`@@ -1184,6 +1184,9 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)`
`1184`	`1184`	`return;`
`1185`	`1185`	`}`
`1186`	`1186`	`mutex_unlock(&master->bus_lock_mutex);`
	`1187`	`+`
	`1188`	`+ /* Prod the scheduler in case transfer_one() was busy waiting */`
	`1189`	`+ cond_resched();`
`1187`	`1190`	`}`
`1188`	`1191`
`1189`	`1192`	`/**`