From: zhang.lei@jp.fujitsu.com (Zhang, Lei)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH]irqchip/irq-gic-v3:Avoid a waste of LPI resource
Date: Fri, 27 Apr 2018 14:00:44 +0000 [thread overview]
Message-ID: <8898674D84E3B24BA3A2D289B872026A69EED0B0@G01JPEXMBKW03> (raw)
I want to talk about the implementation of GIC-ITS driver.
The current implementation of irq-gic-v3-its driver allocates at least 32 LPIs (interrupt numbers) for each Device ID even if the number of requested LPIs is only one.
I think it is a waste for LPI resource.
And if we use many devices over ITS, this implementation may cause a shortage of LPI .
I have a patch to avoid this problem by reducing the number of LPIs from 32 to 2 per chunk.
The points of this patch are as follows.
Point1:Each Device ID can still allocate enough LPIs by increasing chunk number.
Point2:The size of memory for the bitmap (lpi_bitmap) to manage the free chunks becomes larger(256B -> 4KiB).But I think it is not a problem, because the max size of lpi_bitmap is 4KiB.
Signed-off-by: Lei Zhang <zhang.lei@jp.fujitsu.com>
The follow is my patch. the patch is based on kernel 4.16.5
-------------------------------------
--- drivers/irqchip/irq-gic-v3-its.c 2018-01-29 06:20:33.000000000 +0900
+++ drivers/irqchip/irq-gic-v3-its.c 2018-04-25 15:05:26.078956980 +0900
@@ -1406,12 +1406,12 @@
*
* The GIC has id_bits bits for interrupt identifiers. From there, we
* must subtract 8192 which are reserved for SGIs/PPIs/SPIs. Then, as
- * we allocate LPIs by chunks of 32, we can shift the whole thing by 5
+ * we allocate LPIs by chunks of 2, we can shift the whole thing by 1
* bits to the right.
*
* This gives us (((1UL << id_bits) - 8192) >> 5) possible allocations.
*/
-#define IRQS_PER_CHUNK_SHIFT 5
+#define IRQS_PER_CHUNK_SHIFT 1
#define IRQS_PER_CHUNK (1 << IRQS_PER_CHUNK_SHIFT)
#define ITS_MAX_LPI_NRBITS 16 /* 64K LPIs */
Regards,
Lei Zhang
--
e-mail: zhang.lei@jp.fujitsu.com
next reply other threads:[~2018-04-27 14:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-27 14:00 Zhang, Lei [this message]
[not found] <8898674D84E3B24BA3A2D289B872026A69EECF90@G01JPEXMBKW03>
2018-04-27 14:12 ` [PATCH]irqchip/irq-gic-v3:Avoid a waste of LPI resource Marc Zyngier
2018-04-30 7:53 ` Zhang, Lei
2018-04-30 10:20 ` Marc Zyngier
2018-05-03 6:46 ` Zhang, Lei
2018-05-09 14:32 ` Mark Langsdorf
2018-05-10 13:09 ` Zhang, Lei
2018-05-10 14:12 ` Marc Zyngier
2018-05-12 1:47 ` Zhang, Lei
2018-05-18 9:49 ` Zhang, Lei
2018-05-21 6:12 ` Zhang, Lei
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