From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C369626A0A4; Thu, 13 Mar 2025 17:09:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741885791; cv=none; b=PCGkN0zNpYkUhTKjS0SR1gpTr74DCjxbmXFnVFJnD1+6Rffj96TRnuisFZyzhpXFvv82AVZqwIDu2orA08DcmxoVgirhUkPQp/Qjqbaj87T+mec4BjSrgkCTAn9v3iVAPIWi6GRrPRax7i1jT/EEFwomKKcsNmPak4+IvrwkHdI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741885791; c=relaxed/simple; bh=sAqPeaaP78JXfLlIvaZj0VRL43aWerSGG4s5j0yVKS0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S2a1+DuHExHGr9bsRCzlBg00/WIqlVoRs48FvhHT2I+z6o/OwX07ek4WvNyZ3RG9g65N7umIX9bq7nuXgAxN2zfVUJIgKps05v3wSdZgFDHgqXUZITmJy/EGKBiNZ2Y/4xUUjn5vCD2IovGShFzb3h9mFm8XZDRGirv7DAlEGvU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JIddFRKe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JIddFRKe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9AE2FC4CEE9; Thu, 13 Mar 2025 17:09:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741885791; bh=sAqPeaaP78JXfLlIvaZj0VRL43aWerSGG4s5j0yVKS0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JIddFRKel0caC56WFEnasFaM9S0AIIOHInn/ADrJkrwLPYgTZbsw/OqYsyeiGzFf6 6V+bNm3J/6bFtFhjWoyAZWr4NgYFLJmG3hZXrUqvoNho1by8oLb2j+8PmWfu1k9zBI jsC14SepH+lVbpztAqfuDXSGITQOa+xqyydCsoPm6ovRNN1Hb438gZM5fzA5kny7Q4 hGmRXlJHQgOc/+wdFnZ4gZ+9nzZfUJrGhyHnYy7T647jFNIB/Ap80rTXqGFtWwg4EK JtjUHFKWtLVRJkfOBpytGx5maa9pJAv4UGJgStpIRknBTvHWW2FkVC1fVR/CF9bLi2 8/4jFFBS30gfQ== Date: Thu, 13 Mar 2025 18:09:45 +0100 From: Ingo Molnar To: Tao Chen Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll Message-ID: References: <20250313051047.2436098-1-chen.dylane@linux.dev> <87b67a79-d97e-4f81-9bf2-aa34d613b5bf@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87b67a79-d97e-4f81-9bf2-aa34d613b5bf@linux.dev> * Tao Chen wrote: > 在 2025/3/13 18:05, Ingo Molnar 写道: > > > > * Tao Chen wrote: > > > > > The poll man page says POLLRDNORM is equivalent to POLLIN, > > > so add EPOLLRDNORM here. > > > > > > Signed-off-by: Tao Chen > > > --- > > > kernel/events/ring_buffer.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > > > index 59a52b1a1..5130b119d 100644 > > > --- a/kernel/events/ring_buffer.c > > > +++ b/kernel/events/ring_buffer.c > > > @@ -19,7 +19,7 @@ > > > static void perf_output_wakeup(struct perf_output_handle *handle) > > > { > > > - atomic_set(&handle->rb->poll, EPOLLIN); > > > + atomic_set(&handle->rb->poll, EPOLLIN | EPOLLRDNORM); > > > > So what does EPOLLRDNORM mean to begin with? There doesn't seem to be > > separate/specific handling of it anywhere in the kernel that I can > > see... > > > > It seems that if user set pollfd with POLLRDNORM, perf_poll will not return > until timeout even if perf_output_wakeup called, whereas POLLIN returns. Mind adding this to the changelog, and explain that this patch fixes this particular poll() functionality and semantics for userspace? Thanks, Ingo