linux-kernel - Re: [PATCH V5 9/9] coresight: etm-perf: incorporating sink definition from cmd line

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Date:   Tue, 23 Aug 2016 08:46:59 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        jolsa@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Vince Weaver <vince@...ter.net>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V5 9/9] coresight: etm-perf: incorporating sink definition
 from cmd line

On 22 August 2016 at 10:40, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>
>> +enum {
>> +     ETM_TOKEN_SINK_CPU,
>> +     ETM_TOKEN_SINK,
>> +     ETM_TOKEN_ERR,
>> +};
>> +
>> +static const match_table_t drv_cfg_tokens = {
>> +     {ETM_TOKEN_SINK_CPU, "sink=cpu%d:%s"},
>> +     {ETM_TOKEN_SINK, "sink=%s"},
>> +     {ETM_TOKEN_ERR, NULL},
>> +};
>
> Wait, but we just parsed away the '=' and the whole thing is now a
> linked list of { key, value }?

You're correct.  From a parsing point of view it was better to
reassemble the string and parse the whole thing again.  As suggested
in my previous email if the parsing for "sink=xyz"  is done in the
core we won't have to do this part.

>
> This also answers my question from the other email about the use cases
> for sending in ascii strings. In my opinion, all this is completely
> unnecessary.
>
>> +static int
>> +etm_set_drv_configs(struct perf_event *event,
>> +                 struct list_head *drv_configs)
>> +{
>> +     char *config, *sink;
>> +     int len;
>> +     struct perf_drv_config *drv_config;
>> +     void *old_sink;
>> +
>> +     list_for_each_entry(drv_config, drv_configs, entry) {
>> +             /* ETM HW configuration needs a sink specification */
>> +             if (!drv_config->option)
>> +                     return -EINVAL;
>> +
>> +             len = strlen(drv_config->config) + strlen("=") +
>> +                   strlen(drv_config->option) + 1;
>> +
>> +             config = kmalloc(len, GFP_KERNEL);
>> +             if (!config)
>> +                     return -ENOMEM;
>> +
>> +             /* Reconstruct user configuration */
>> +             snprintf(config, len, "%s=%s",
>> +                      drv_config->config, drv_config->option);
>
> Wait, what? We parse this *twice*?
>
> There's basically a malloc+snprintf[which could have been
> kasprintf()]+match_token just to see if drv_config::option starts with a
> 'cpu%d:'?
>
> Regards,
> --
> Alex