linux-kernel - Re: [PATCH v2 10/13] perf header: add a buffer to struct feat

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Date:   Thu, 25 May 2017 10:09:17 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v2 10/13] perf header: add a buffer to struct feat_fd

On Tue, May 23, 2017 at 12:48:50AM -0700, David Carrillo-Cisneros wrote:

SNIP

> @@ -795,11 +831,19 @@ static int write_pmu_mappings(struct feat_fd *fd,
>  			      struct perf_evlist *evlist __maybe_unused)
>  {
>  	struct perf_pmu *pmu = NULL;
> -	off_t offset = lseek(fd->fd, 0, SEEK_CUR);
> -	__u32 pmu_num = 0;
> +	u32 pmu_num = 0;
>  	int ret;
>  
> -	/* write real pmu_num later */
> +	/*
> +	 * Do a first pass to count number of pmu to avoid lseek so this
> +	 * works in pipe mode as well.
> +	 */
> +	while ((pmu = perf_pmu__scan(pmu))) {
> +		if (!pmu->name)
> +			continue;
> +		pmu_num++;
> +	}

please put this functionality into preceeding separate patch

thanks,
jirka