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Message-Id: <20240917-blktrace-algn-v1-1-9fb54b7b1dfa@samsung.com>
Date: Tue, 17 Sep 2024 17:22:18 +0200
From: Daniel Gomez via B4 Relay <devnull+da.gomez.samsung.com@...nel.org>
To: Jens Axboe <axboe@...nel.dk>, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, gost.dev@...sung.com,
John Garry <john.g.garry@...cle.com>, Dave Chinner <dchinner@...hat.com>,
Luis Chamberlain <mcgrof@...nel.org>, Pankaj Raghav <p.raghav@...sung.com>,
Dan Helmick <dan.helmick@...sung.com>, Daniel Gomez <d@...ces.com>,
Daniel Gomez <da.gomez@...sung.com>
Subject: [PATCH RFC] blktrace: add i/o alignment information
From: Daniel Gomez <da.gomez@...sung.com>
This patch introduces max I/O alignment boundaries in terms of LBA and
size in blktrace for issued I/Os.
Tracing alignment information is important for high-capacity and QLC
SSDs with Indirection Units greater than 4 KiB. These devices are still
4 KiB in Logical Block Size (LBS) but because they work at higher IUs,
unaligned writes to the IU boundaries can imply in a read-modify-write
(RMW).
This patch enables blktrace to report alignment details via new
alignment parameter, which will be calculated during I/O tracing.
Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
---
This patch introduces support for tracing maximum I/O alignment
boundaries in terms of Logical Block Addressing (LBA) and size within
blktrace for issued I/Os.
Note: the term alignment has been previously discussed here [1], where
it was suggested to use "largest block size granularity". In this RFC,
alignment term is kept, though further suggestions for an appropriate
term are welcomed.
[1] https://lore.kernel.org/all/a7f9079f-6f47-4a47-a327-98497bd33dfe@oracle.com
Tracing alignment information is important for high-capacity and QLC
SSDs with Indirection Units greater than 4 KiB. These devices are still
4 KiB in Logical Block Size (LBS) but because they work at higher IUs,
unaligned writes to the IU boundaries can imply in a read-modify-write
(RMW).
More information about the motivation can be found in the first LBS
patch series [2].
[2] Subject: [RFC 00/23] Enable block size > page size in XFS
https://lore.kernel.org/lkml/20230915183848.1018717-1-kernel@pankajraghav.com/
Additionally, Dan Helmick's talk [3] provides further context on the
importance of I/O granularity and alignment, specifically in the context
of NVMe.
[3] SDC2022 – Optimal Performance Parameters for NVMe SSDs
The graph below is a representation of the device IU vs what is
considered here the I/O block alignment.
|--- IU Boundaries ----| |-PS-|
a) [====][====][====][====][····][····][····]--
| |
b) [····][====][====][====][====][····][····]--
| |
c) [····][····][====][====][····][····][····]--
| |
LBA 0 4
Key:
[====] = I/O Block
[····] = Memory in Page Size (PS) chunks
PS: System base Page Size (e.g. x86_64 is 4 KiB)
a) I/O matches IU boundaries (LBA and block size). I/O is aligned to
IU boundaries.
b) The size of the I/O matches the IU size but the I/O is not aligned to
the IU boundaries. I/O is unaligned.
c) I/O does not match in either size or LBA. I/O is unaligned.
This patch enables blktrace to report alignment details via new
alignment parameter, which will be calculated during I/O tracing. For
the example above, the following values would be reported:
a) |16384|: I/O aligned to 16 KiB boundaries.
b) |4096|: I/O aligned to 4 KiB boundaries.
c) |8192|: I/O aligned to 8 KiB boundaries.
Finally, this patch requires some minor changes [4] in the blktrace
tool. If this moves forward, the changes will be submitted accordingly.
[4] https://github.com/dkruces/blktrace/tree/algn
---
include/linux/blktrace_api.h | 2 ++
include/uapi/linux/blktrace_api.h | 1 +
kernel/trace/blktrace.c | 38 ++++++++++++++++++++++++++++++++++++++
3 files changed, 41 insertions(+)
diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index 122c62e561fc..17f1a21ffb5a 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -26,6 +26,8 @@ struct blk_trace {
struct dentry *dir;
struct list_head running_list;
atomic_t dropped;
+ u32 lbs;
+ u8 lba_shift;
};
extern int blk_trace_ioctl(struct block_device *, unsigned, char __user *);
diff --git a/include/uapi/linux/blktrace_api.h b/include/uapi/linux/blktrace_api.h
index 690621b610e5..d6df0c10ece1 100644
--- a/include/uapi/linux/blktrace_api.h
+++ b/include/uapi/linux/blktrace_api.h
@@ -110,6 +110,7 @@ struct blk_io_trace {
__u32 cpu; /* on what cpu did it happen */
__u16 error; /* completion error */
__u16 pdu_len; /* length of data after this trace */
+ __u32 alignment; /* i/o alignment boundaries */
/* cgroup id will be stored here if exists */
};
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 8fd292d34d89..8330455458b8 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -208,6 +208,39 @@ static const u32 ddir_act[2] = { BLK_TC_ACT(BLK_TC_READ),
#define MASK_TC_BIT(rw, __name) ((__force u32)(rw & REQ_ ## __name) << \
(ilog2(BLK_TC_ ## __name) + BLK_TC_SHIFT - __REQ_ ## __name))
+static inline bool blk_trace_lba_aligned(u32 len, u32 algn_len, u64 lba,
+ u32 algn_lba)
+{
+ return !(len % algn_len) && !(lba % algn_lba);
+}
+
+static inline u32 blk_trace_align(struct blk_trace *bt, u64 sector,
+ u32 len)
+{
+ u64 lba = sector >> (bt->lba_shift - SECTOR_SHIFT);
+ u32 align_len = len;
+ u32 align_lba = align_len / bt->lbs;
+ u32 alignment = bt->lbs;
+
+ if (is_power_of_2(len) &&
+ blk_trace_lba_aligned(len, align_len, lba, align_lba))
+ return len;
+
+ align_len = bt->lbs << 1UL;
+ align_lba = align_len / bt->lbs;
+
+ while (align_len < len) {
+ if (!blk_trace_lba_aligned(len, align_len, lba, align_lba))
+ break;
+
+ alignment = align_len;
+ align_len = align_len << 1UL;
+ align_lba = align_len / bt->lbs;
+ }
+
+ return alignment;
+}
+
/*
* The worker for the various blk_add_trace*() types. Fills out a
* blk_io_trace structure and places it in a per-cpu subbuffer.
@@ -296,6 +329,9 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
t->device = bt->dev;
t->error = error;
t->pdu_len = pdu_len + cgid_len;
+ if (((what & 0xffff) & ~__BLK_TA_CGROUP) == __BLK_TA_ISSUE)
+ t->alignment =
+ blk_trace_align(bt, sector, bytes);
if (cgid_len)
memcpy((void *)t + sizeof(*t), &cgid, cgid_len);
@@ -597,6 +633,8 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
bt->act_mask = (u16) -1;
blk_trace_setup_lba(bt, bdev);
+ bt->lbs = queue_logical_block_size(q);
+ bt->lba_shift = ilog2(bt->lbs);
/* overwrite with user settings */
if (buts->start_lba)
---
base-commit: 4f3e012d4cfd1d9bf837870c961f462ca9f23ebe
change-id: 20240916-blktrace-algn-a11320353182
Best regards,
--
Daniel Gomez <da.gomez@...sung.com>
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