* [PATCH] iov_iter: optimise bvec iov_iter_advance()
@ 2020-12-03 1:45 Pavel Begunkov
2020-12-03 9:14 ` Christoph Hellwig
0 siblings, 1 reply; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-03 1:45 UTC (permalink / raw)
To: Alexander Viro; +Cc: linux-fsdevel, linux-kernel
iov_iter_advance() is heavily used, but implemented through generic
iteration. As bvecs have a specifically crafted advance() function, i.e.
bvec_iter_advance(), which is faster and slimmer, use it instead.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
lib/iov_iter.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 1635111c5bd2..7fbdd9ef3ff0 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1077,6 +1077,20 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
i->count -= size;
return;
}
+ if (iov_iter_is_bvec(i)) {
+ struct bvec_iter bi;
+
+ bi.bi_size = i->count;
+ bi.bi_bvec_done = i->iov_offset;
+ bi.bi_idx = 0;
+ bvec_iter_advance(i->bvec, &bi, size);
+
+ i->bvec += bi.bi_idx;
+ i->nr_segs -= bi.bi_idx;
+ i->count = bi.bi_size;
+ i->iov_offset = bi.bi_bvec_done;
+ return;
+ }
iterate_and_advance(i, size, v, 0, 0, 0)
}
EXPORT_SYMBOL(iov_iter_advance);
--
2.24.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] iov_iter: optimise bvec iov_iter_advance()
2020-12-03 1:45 [PATCH] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
@ 2020-12-03 9:14 ` Christoph Hellwig
2020-12-03 11:48 ` Pavel Begunkov
0 siblings, 1 reply; 5+ messages in thread
From: Christoph Hellwig @ 2020-12-03 9:14 UTC (permalink / raw)
To: Pavel Begunkov; +Cc: Alexander Viro, linux-fsdevel, linux-kernel
> @@ -1077,6 +1077,20 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
> i->count -= size;
> return;
> }
> + if (iov_iter_is_bvec(i)) {
> + struct bvec_iter bi;
> +
> + bi.bi_size = i->count;
> + bi.bi_bvec_done = i->iov_offset;
> + bi.bi_idx = 0;
> + bvec_iter_advance(i->bvec, &bi, size);
> +
> + i->bvec += bi.bi_idx;
> + i->nr_segs -= bi.bi_idx;
> + i->count = bi.bi_size;
> + i->iov_offset = bi.bi_bvec_done;
> + return;
> + }
> iterate_and_advance(i, size, v, 0, 0, 0)
I like the idea, but whu not avoid the on-stack bvec_iter and just
open code this entirely using a new helper? E.g.
static void bio_iov_iter_advance(struct iov_iter *i, size_t bytes)
{
unsigned int cnt;
i->count -= bytes;
bytes += i->iov_offset;
for (cnt = 0; bytes && bytes >= i->bvec[cnt].bv_len; cnt++)
bytes -= i->bvec[cnt].bv_len;
i->iov_offset = bytes;
i->bvec += cnt;
i->nr_segs -= cnt;
}
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] iov_iter: optimise bvec iov_iter_advance()
2020-12-03 9:14 ` Christoph Hellwig
@ 2020-12-03 11:48 ` Pavel Begunkov
2020-12-09 8:33 ` Christoph Hellwig
0 siblings, 1 reply; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-03 11:48 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Alexander Viro, linux-fsdevel, linux-kernel
On 03/12/2020 09:14, Christoph Hellwig wrote:
>> @@ -1077,6 +1077,20 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
>> i->count -= size;
>> return;
>> }
>> + if (iov_iter_is_bvec(i)) {
>> + struct bvec_iter bi;
>> +
>> + bi.bi_size = i->count;
>> + bi.bi_bvec_done = i->iov_offset;
>> + bi.bi_idx = 0;
>> + bvec_iter_advance(i->bvec, &bi, size);
>> +
>> + i->bvec += bi.bi_idx;
>> + i->nr_segs -= bi.bi_idx;
>> + i->count = bi.bi_size;
>> + i->iov_offset = bi.bi_bvec_done;
>> + return;
>> + }
>> iterate_and_advance(i, size, v, 0, 0, 0)
>
> I like the idea, but whu not avoid the on-stack bvec_iter and just
> open code this entirely using a new helper? E.g.
It's inlined and the on-stack iter is completely optimised out. Frankly,
I'd rather not open-code bvec_iter_advance(), at least for this chunk to
be findable from bvec.h, e.g. grep bvec_iter and bvec_for_each. Though,
I don't like myself that preamble/postamble.
>
> static void bio_iov_iter_advance(struct iov_iter *i, size_t bytes)
> {
> unsigned int cnt;
>
> i->count -= bytes;
>
> bytes += i->iov_offset;
> for (cnt = 0; bytes && bytes >= i->bvec[cnt].bv_len; cnt++)
> bytes -= i->bvec[cnt].bv_len;
> i->iov_offset = bytes;
>
> i->bvec += cnt;
> i->nr_segs -= cnt;
> }
>
--
Pavel Begunkov
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] iov_iter: optimise bvec iov_iter_advance()
2020-12-03 11:48 ` Pavel Begunkov
@ 2020-12-09 8:33 ` Christoph Hellwig
2020-12-09 12:06 ` Pavel Begunkov
0 siblings, 1 reply; 5+ messages in thread
From: Christoph Hellwig @ 2020-12-09 8:33 UTC (permalink / raw)
To: Pavel Begunkov
Cc: Christoph Hellwig, Alexander Viro, linux-fsdevel, linux-kernel
On Thu, Dec 03, 2020 at 11:48:56AM +0000, Pavel Begunkov wrote:
> It's inlined and the on-stack iter is completely optimised out. Frankly,
> I'd rather not open-code bvec_iter_advance(), at least for this chunk to
> be findable from bvec.h, e.g. grep bvec_iter and bvec_for_each. Though,
> I don't like myself that preamble/postamble.
Ok. I still think we at least want a separate helper instead of
bloating the main iov_iter_advance.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] iov_iter: optimise bvec iov_iter_advance()
2020-12-09 8:33 ` Christoph Hellwig
@ 2020-12-09 12:06 ` Pavel Begunkov
0 siblings, 0 replies; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-09 12:06 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Alexander Viro, linux-fsdevel, linux-kernel
On 09/12/2020 08:33, Christoph Hellwig wrote:
> On Thu, Dec 03, 2020 at 11:48:56AM +0000, Pavel Begunkov wrote:
>> It's inlined and the on-stack iter is completely optimised out. Frankly,
>> I'd rather not open-code bvec_iter_advance(), at least for this chunk to
>> be findable from bvec.h, e.g. grep bvec_iter and bvec_for_each. Though,
>> I don't like myself that preamble/postamble.
>
> Ok. I still think we at least want a separate helper instead of
> bloating the main iov_iter_advance.
I agree on that, just haven't got back to it yet.
--
Pavel Begunkov
^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-12-03 1:45 [PATCH] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2020-12-03 9:14 ` Christoph Hellwig
2020-12-03 11:48 ` Pavel Begunkov
2020-12-09 8:33 ` Christoph Hellwig
2020-12-09 12:06 ` Pavel Begunkov
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