Re: a strlen update

From: Timothe Litt <litt_at_acm.org>
Date: Mon, 14 Feb 2022 06:08:09 -0500

free() seems odd.  Since they vastly outnumber (malloc+calloc+realloc),
likely many (most?) are free(NULL) -- e.g. clean up paths where
something might have been allocated.

If this is the case, they're relatively cheap - the call overhead + an
early check for NULL arg.

The 1 byte memcpy is worth a look.  If it's copying null (zero-length)
strings, the strlen work could allow replacement with a
test/assignment.  memcpy is not likely to be optimized for that case. 
It tends to be optimized for longer moves.

It would not be surprising if both are in openssl/nghttp2 rather than
cURL proper.

You may be able to eliminate the clock_gettime calls if no one is
looking at timing, which is probably a common case for library users. 
(For the command, !(verbose|progress|?timeouts?), but progress is a
default.)  They are relatively inexpensive syscalls, frequently
optmized, but may involve a mode change and a lock (depending on
architecture and OS).  But you may need an API change (e.g. in
global_init or setopt) to disable statistics.

In all three cases, look at the actual performance impact - the return
on fixing these may be low.

Timothe Litt
ACM Distinguished Engineer
--------------------------
This communication may not represent the ACM or my employer's views,
if any, on the matters discussed.

On 14-Feb-22 03:33, Daniel Stenberg via curl-library wrote:
> Other fun observations running this same command line:
>
> The top-25 lib calls done:
>
>    2239 free
>     635 malloc
>     545 memcpy
>     300 memchr
>     245 strcmp
>     225 strlen
>     162 inet_pton
>     134 clock_gettime
>     110 OPENSSL_sk_value
>     110 ASN1_STRING_length
>     110 ASN1_STRING_get0_data
>      75 strdup
>      63 sigaction
>      56 calloc
>      50 nghttp2_session_get_stream_user_data
>      38 realloc
>      37 ERR_clear_error
>      36 strchr
>      31 poll
>      31 nghttp2_session_want_read
>      28 nghttp2_session_send
>      26 nghttp2_session_mem_recv
>      26 nghttp2_session_check_request_allowed
>      25 getenv
>      24 SSL_set_ex_data
>
> Those 545 memcpy() calls are interesting because 384 of them copy only
> a single byte!
>

-- 
Unsubscribe: https://lists.haxx.se/listinfo/curl-library
Etiquette:   https://curl.haxx.se/mail/etiquette.html

Received on 2022-02-14