On 6/22/21 1:14 PM, Dan Williams wrote:
On Fri, 2021-06-18 at 21:49 +0200, Dumitru Ceara wrote:
On 6/4/21 10:00 PM, Dan Williams wrote:
Inspried by:
3b6362d64e86b northd: Avoid memory reallocation while building lb
rules.
Signed-off-by: Dan Williams <[email protected]>
---
NOTE: this is driven by visual inspection not perf data. But it
shouldn't be worse than current code and should be better for
large numbers of ACLs I think.
The changes look OK to me.
Acked-by: Dumitru Ceara <[email protected]>
However, I wonder how many such optimizations we can implement
without
affecting maintainability. Mark suggested an approach [0].
I'm happy to drop my patch in favor of Mark's. I think mine is a subset
of his.
Dan
Funny because I'm not even 100% behind my own approach.
CC-ing Ilya too, maybe he has some more suggestions, maybe there's a
way
to better use the OVS dynamic strings.
I did some brainstorming and came up with a test program:
#include <stdio.h>
#include <stdarg.h>
static void
my_crazy_printf(char *fmt1, char *fmt2, ...)
{
va_list ap;
va_start(ap, fmt2);
vprintf(fmt1, ap);
va_list aq;
va_copy(aq, ap);
vprintf(fmt2, aq);
va_end(aq);
va_end(ap);
}
int main(void)
{
my_crazy_printf("%s=%d\n", "%s=%d\n", "howdy", 4, "byebye", 3);
return 0;
}
On my system, the output is:
howdy=4
byebye=3
I came up with this as a test to see how feasible it is to have two
format strings in the same parameter list. The idea here is to translate
that into something like this:
/* I've omitted unimportant parameters */
static void
ovn_lflow_add(match_fmt, actions_fmt, ...)
{
static struct ds match = DS_EMPTY_INITIALIZER;
static struct ds actions = DS_EMPTY_INITIALIZER;
struct va_list ap;
va_start(ap, actions_fmt);
ds_clear(&match);
ds_put_format_valist(&match, match_fmt, ap);
struct va_list aq;
va_copy(aq, ap);
ds_clear(&actions);
ds_put_format_valist(&match, actions_fmt, aq);
va_end(aq);
va_end(ap);
/* The rest of the function */
}
With this, the dynamic string handling is done entirely within
ovn_lflow_add(), meaning that the same buffers are reused. The problem
(aside from the fact that it's weird), is that ds_put_format_valist()
performs its own va_copy() operation of the passed-in va_list. This
means that the two ds_put_format_valist() operations operate on
identical va_lists. Pursuing this problem any further means essentially
re-implementing dynamic strings to allow for this unorthodox usage. It
feels like a dead end to me.
Regards,
Dumitru
[0]
https://mail.openvswitch.org/pipermail/ovs-dev/2021-June/384043.html
[1] Test code:
If you run this code, then the output is:
howdy=4
byebye=3
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