From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1av35R-0005ic-Cz for mharc-qemu-trivial@gnu.org; Tue, 26 Apr 2016 09:31:33 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45467) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1auyKF-0001JV-2r for qemu-trivial@nongnu.org; Tue, 26 Apr 2016 04:26:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1auyKE-0004p6-27 for qemu-trivial@nongnu.org; Tue, 26 Apr 2016 04:26:31 -0400 Received: from [59.151.112.132] (port=50200 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1auyK7-0004oX-W6; Tue, 26 Apr 2016 04:26:24 -0400 X-IronPort-AV: E=Sophos;i="5.22,518,1449504000"; d="scan'208";a="5963910" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 26 Apr 2016 16:26:20 +0800 Received: from G08CNEXCHPEKD01.g08.fujitsu.local (unknown [10.167.33.80]) by cn.fujitsu.com (Postfix) with ESMTP id 7F60B408D29C; Tue, 26 Apr 2016 16:26:19 +0800 (CST) Received: from [10.167.226.49] (10.167.226.49) by G08CNEXCHPEKD01.g08.fujitsu.local (10.167.33.89) with Microsoft SMTP Server id 14.3.279.2; Tue, 26 Apr 2016 16:26:19 +0800 To: Christian Borntraeger , References: <1461633961-31713-1-git-send-email-zhoujie2011@cn.fujitsu.com> <571F1CA4.70306@de.ibm.com> CC: , From: Zhou Jie Message-ID: <571F262A.3020705@cn.fujitsu.com> Date: Tue, 26 Apr 2016 16:26:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <571F1CA4.70306@de.ibm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-yoursite-MailScanner-ID: 7F60B408D29C.AE47B X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: zhoujie2011@cn.fujitsu.com X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 59.151.112.132 X-Mailman-Approved-At: Tue, 26 Apr 2016 09:31:31 -0400 Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] net/tap: Allocating Large sized arrays to heap X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Apr 2016 08:26:32 -0000 On 2016/4/26 15:45, Christian Borntraeger wrote: > On 04/26/2016 03:26 AM, Zhou Jie wrote: >> net_init_tap has a huge stack usage of 8192 bytes approx. >> Moving large arrays to heap to reduce stack usage. > > I am wondering. Why is 8k a problem for a user space program? For 64bit machine it will be 16k. > Please note that malloc/new like allocations are much more expensive > than stack allocation in terms of performance. This does not matter > here, but in your other patch that deals with the xmit function, I would > not be surprised if that actually harms performance. OK. I will note it. Sincerely, Zhou Jie > > Christian > > > >> >> Signed-off-by: Zhou Jie >> --- >> net/tap.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/net/tap.c b/net/tap.c >> index 740e8a2..49817c7 100644 >> --- a/net/tap.c >> +++ b/net/tap.c >> @@ -769,8 +769,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name, >> return -1; >> } >> } else if (tap->has_fds) { >> - char *fds[MAX_TAP_QUEUES]; >> - char *vhost_fds[MAX_TAP_QUEUES]; >> + char **fds = g_new(char *, MAX_TAP_QUEUES); >> + char **vhost_fds = g_new(char *, MAX_TAP_QUEUES); >> int nfds, nvhosts; >> >> if (tap->has_ifname || tap->has_script || tap->has_downscript || >> @@ -818,6 +818,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name, >> return -1; >> } >> } >> + g_free(fds); >> + g_free(vhost_fds); >> } else if (tap->has_helper) { >> if (tap->has_ifname || tap->has_script || tap->has_downscript || >> tap->has_vnet_hdr || tap->has_queues || tap->has_vhostfds) { >> > > > > -- ------------------------------------------------ 周潔 Dept 1 No. 6 Wenzhu Road, Nanjing, 210012, China TEL：+86+25-86630566-8557 FUJITSU INTERNAL：7998-8557 E-Mail：zhoujie2011@cn.fujitsu.com ------------------------------------------------ From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45450) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1auyKD-0001Gs-3i for qemu-devel@nongnu.org; Tue, 26 Apr 2016 04:26:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1auyK8-0004of-Ep for qemu-devel@nongnu.org; Tue, 26 Apr 2016 04:26:29 -0400 References: <1461633961-31713-1-git-send-email-zhoujie2011@cn.fujitsu.com> <571F1CA4.70306@de.ibm.com> From: Zhou Jie Message-ID: <571F262A.3020705@cn.fujitsu.com> Date: Tue, 26 Apr 2016 16:26:18 +0800 MIME-Version: 1.0 In-Reply-To: <571F1CA4.70306@de.ibm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] net/tap: Allocating Large sized arrays to heap List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger , qemu-devel@nongnu.org Cc: qemu-trivial@nongnu.org, jasowang@redhat.com On 2016/4/26 15:45, Christian Borntraeger wrote: > On 04/26/2016 03:26 AM, Zhou Jie wrote: >> net_init_tap has a huge stack usage of 8192 bytes approx. >> Moving large arrays to heap to reduce stack usage. > > I am wondering. Why is 8k a problem for a user space program? For 64bit machine it will be 16k. > Please note that malloc/new like allocations are much more expensive > than stack allocation in terms of performance. This does not matter > here, but in your other patch that deals with the xmit function, I would > not be surprised if that actually harms performance. OK. I will note it. Sincerely, Zhou Jie > > Christian > > > >> >> Signed-off-by: Zhou Jie >> --- >> net/tap.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/net/tap.c b/net/tap.c >> index 740e8a2..49817c7 100644 >> --- a/net/tap.c >> +++ b/net/tap.c >> @@ -769,8 +769,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name, >> return -1; >> } >> } else if (tap->has_fds) { >> - char *fds[MAX_TAP_QUEUES]; >> - char *vhost_fds[MAX_TAP_QUEUES]; >> + char **fds = g_new(char *, MAX_TAP_QUEUES); >> + char **vhost_fds = g_new(char *, MAX_TAP_QUEUES); >> int nfds, nvhosts; >> >> if (tap->has_ifname || tap->has_script || tap->has_downscript || >> @@ -818,6 +818,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name, >> return -1; >> } >> } >> + g_free(fds); >> + g_free(vhost_fds); >> } else if (tap->has_helper) { >> if (tap->has_ifname || tap->has_script || tap->has_downscript || >> tap->has_vnet_hdr || tap->has_queues || tap->has_vhostfds) { >> > > > > -- ------------------------------------------------ 周潔 Dept 1 No. 6 Wenzhu Road, Nanjing, 210012, China TEL：+86+25-86630566-8557 FUJITSU INTERNAL：7998-8557 E-Mail：zhoujie2011@cn.fujitsu.com ------------------------------------------------