linux-kernel - [PATCH] blk-iocost: avoid 64-bit division in ioc_timer

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Message-Id: <20230118080706.3303186-1-arnd@kernel.org>
Date:   Wed, 18 Jan 2023 09:07:01 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     Arnd Bergmann <arnd@...db.de>, Kemeng Shi <shikemeng@...wei.com>,
        Andreas Herrmann <aherrmann@...e.de>,
        Yu Kuai <yukuai3@...wei.com>,
        Chengming Zhou <zhouchengming@...edance.com>,
        Jinke Han <hanjinke.666@...edance.com>,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] blk-iocost: avoid 64-bit division in ioc_timer_fn

From: Arnd Bergmann <arnd@...db.de>

The behavior of 'enum' types has changed in gcc-13, so now the
UNBUSY_THR_PCT constant is interpreted as a 64-bit number because
it is defined as part of the same enum definition as some other
constants that do not fit within a 32-bit integer. This in turn
leads to some inefficient code on 32-bit architectures as well
as a link error:

arm-linux-gnueabi/bin/arm-linux-gnueabi-ld: block/blk-iocost.o: in function `ioc_timer_fn':
blk-iocost.c:(.text+0x68e8): undefined reference to `__aeabi_uldivmod'
arm-linux-gnueabi-ld: blk-iocost.c:(.text+0x6908): undefined reference to `__aeabi_uldivmod'

Split the enum definition to keep the 64-bit timing constants in
a separate enum type from those constants that can clearly fit
within a smaller type.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 block/blk-iocost.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 6955605629e4..b691b6bb498f 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -258,6 +258,11 @@ enum {
 	VRATE_MIN		= VTIME_PER_USEC * VRATE_MIN_PPM / MILLION,
 	VRATE_CLAMP_ADJ_PCT	= 4,
 
+	/* switch iff the conditions are met for longer than this */
+	AUTOP_CYCLE_NSEC	= 10LLU * NSEC_PER_SEC,
+};
+
+enum {
 	/* if IOs end up waiting for requests, issue less */
 	RQ_WAIT_BUSY_PCT	= 5,
 
@@ -296,9 +301,6 @@ enum {
 	/* don't let cmds which take a very long time pin lagging for too long */
 	MAX_LAGGING_PERIODS	= 10,
 
-	/* switch iff the conditions are met for longer than this */
-	AUTOP_CYCLE_NSEC	= 10LLU * NSEC_PER_SEC,
-
 	/*
 	 * Count IO size in 4k pages.  The 12bit shift helps keeping
 	 * size-proportional components of cost calculation in closer
-- 
2.39.0