From: Christoph Hellwig <hch@infradead.org>
To: dsterba@suse.cz, Christoph Hellwig <hch@infradead.org>,
David Sterba <dsterba@suse.com>,
linux-btrfs@vger.kernel.org,
"Gustavo A . R . Silva" <gustavoars@kernel.org>
Subject: Re: [PATCH] btrfs: add special case to setget helpers for 64k pages
Date: Mon, 5 Jul 2021 09:33:34 +0100 [thread overview]
Message-ID: <YOLD3CJjDgiq+kfR@infradead.org> (raw)
In-Reply-To: <20210702110630.GE2610@twin.jikos.cz>
On Fri, Jul 02, 2021 at 01:06:30PM +0200, David Sterba wrote:
> On Fri, Jul 02, 2021 at 08:10:50AM +0100, Christoph Hellwig wrote:
> > > + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> > > return get_unaligned_le##bits(token->kaddr + oip); \
> > > + } else { \
> >
> > No need for an else after the return and thus no need for all the
> > reformatting.
>
> That leads to worse code, compiler does not eliminate the block that
> would otherwise be in the else block. Measured on x86_64 with
> instrumented code to force INLINE_EXTENT_BUFFER_PAGES = 1 this adds
> +1100 bytes of code and has impact on stack consumption.
>
> That the code that is in two branches that do not share any code is
> maybe not pretty but the compiler did what I expected. The set/get
> helpers get called a lot and are performance sensitive.
>
> This patch pre (original version), post (with dropped else):
>
> 1156210 19305 14912 1190427 122a1b pre/btrfs.ko
> 1157386 19305 14912 1191603 122eb3 post/btrfs.ko
For the obvious trivial patch (see below) I see the following
difference, which actually makes the simple change smaller:
text data bss dec hex filename
1322580 112183 27600 1462363 16505b fs/btrfs/btrfs.o.hch
1322832 112183 27600 1462615 165157 fs/btrfs/btrfs.o.dave
This is sing the following compiler:
gcc version 10.2.1 20210110 (Debian 10.2.1-6)
---
diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
index 8260f8bb3ff0..a20954f06ec8 100644
--- a/fs/btrfs/struct-funcs.c
+++ b/fs/btrfs/struct-funcs.c
@@ -73,7 +73,7 @@ u##bits btrfs_get_token_##bits(struct btrfs_map_token *token, \
} \
token->kaddr = page_address(token->eb->pages[idx]); \
token->offset = idx << PAGE_SHIFT; \
- if (oip + size <= PAGE_SIZE) \
+ if (INLINE_EXTENT_BUFFER_PAGES == 1 || oip + size <= PAGE_SIZE) \
return get_unaligned_le##bits(token->kaddr + oip); \
\
memcpy(lebytes, token->kaddr + oip, part); \
@@ -94,7 +94,7 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb, \
u8 lebytes[sizeof(u##bits)]; \
\
ASSERT(check_setget_bounds(eb, ptr, off, size)); \
- if (oip + size <= PAGE_SIZE) \
+ if (INLINE_EXTENT_BUFFER_PAGES == 1 || oip + size <= PAGE_SIZE) \
return get_unaligned_le##bits(kaddr + oip); \
\
memcpy(lebytes, kaddr + oip, part); \
@@ -124,7 +124,7 @@ void btrfs_set_token_##bits(struct btrfs_map_token *token, \
} \
token->kaddr = page_address(token->eb->pages[idx]); \
token->offset = idx << PAGE_SHIFT; \
- if (oip + size <= PAGE_SIZE) { \
+ if (INLINE_EXTENT_BUFFER_PAGES == 1 || oip + size <= PAGE_SIZE) { \
put_unaligned_le##bits(val, token->kaddr + oip); \
return; \
} \
@@ -146,7 +146,7 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
u8 lebytes[sizeof(u##bits)]; \
\
ASSERT(check_setget_bounds(eb, ptr, off, size)); \
- if (oip + size <= PAGE_SIZE) { \
+ if (INLINE_EXTENT_BUFFER_PAGES == 1 || oip + size <= PAGE_SIZE) { \
put_unaligned_le##bits(val, kaddr + oip); \
return; \
} \
next prev parent reply other threads:[~2021-07-05 8:34 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 16:00 [PATCH] btrfs: add special case to setget helpers for 64k pages David Sterba
2021-07-01 21:57 ` Gustavo A. R. Silva
2021-07-01 23:59 ` Qu Wenruo
2021-07-02 0:09 ` Gustavo A. R. Silva
2021-07-02 0:21 ` Qu Wenruo
2021-07-02 0:39 ` Gustavo A. R. Silva
2021-07-02 0:39 ` Qu Wenruo
2021-07-02 1:09 ` Gustavo A. R. Silva
2021-07-02 10:22 ` David Sterba
2021-07-02 7:10 ` Christoph Hellwig
2021-07-02 11:06 ` David Sterba
2021-07-05 8:33 ` Christoph Hellwig [this message]
2021-07-08 14:34 ` David Sterba
2021-07-14 23:37 ` Gustavo A. R. Silva
2021-07-28 15:32 ` David Sterba
2021-07-28 16:00 ` David Sterba
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