Talloc sonsidered harmful to performance testing ...

Richard Sharpe realrichardsharpe at gmail.com
Sun Jun 7 12:46:40 MDT 2015

Hi folks,

I have been working with Steve French to implement some POSIX
extenstions for SMB2/3.

I have written code that uses CREATE CONTEXTS to signal that we want
case-sensitive file names and that we want POSIX info returned in an
open response, but I have also extended GET INFO to accept an
SMB2_GETINFO_UNIX type and mapped that onto the standard Samba CIFS
extensions support.

Then I wrote a torture test to compare the performance of:

1. 100,000 CREATE-with-POSIX-semantics plus return POSIX stat and then
close (including delete on close)

2. 100,000 CREATE-with-POSIX-semantics, then GETINFO UNIX_BASIC and
then close (including delete on close)

3. 100,000 CREATE-with-POSIX-semantics of existing file plus return
POSIX stat and then close (and no delete on close)

4. 100,000 CREATE-with-POSIX-semantics, then GETINFO UNIX_BASIC and
then close (and no delete on close)

Here are the results against localhost:

    test: loop-createposix-close
    time: 2015-06-07 11:00:53.685405
    time: 2015-06-07 11:03:41.035283
    success: loop-createposix-close
    test: loop-create-getinfo-close
    time: 2015-06-07 11:03:41.036257
    time: 2015-06-07 11:13:42.639715
    success: loop-create-getinfo-close
    test: loop-openposix-close
    time: 2015-06-07 11:13:42.639761
    time: 2015-06-07 11:16:17.972404
    success: loop-openposix-close
    test: loop-open-getinfo-close
    time: 2015-06-07 11:16:17.972474
    time: 2015-06-07 11:26:35.399646
    success: loop-open-getinfo-close

As you can see, the runs doing GET INFO take seven minutes longer than
the runs without. When it was running smbtorture was getting 90+% of
the CPU (one CPU) and smbd was getting very small amounts of CPU and
was not growing in size at all.

This seems to be because of the following code in smb2_pull_o16s16_blob:

        *blob = data_blob_talloc(mem_ctx, buf->hdr + ofs, size);
        return NT_STATUS_OK;

Does anyone have any comments? If I get a chance I might modify that
code to use any passed in blob if it is big enough.

Attached are my patches.

Richard Sharpe
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