From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933257AbeB1PfR (ORCPT ); Wed, 28 Feb 2018 10:35:17 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54554 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932791AbeB1PfP (ORCPT ); Wed, 28 Feb 2018 10:35:15 -0500 Date: Wed, 28 Feb 2018 17:35:10 +0200 From: "Michael S. Tsirkin" To: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Cc: Linux Kernel Mailing List , Sergio Lopez Pascual , Baoquan He , "Somlo, Gabriel" , xiaolong.ye@intel.com Subject: Re: [PATCH v15 11/11] RFC: fw_cfg: do DMA read operation Message-ID: <20180228173444-mutt-send-email-mst@kernel.org> References: <20180215213312.29234-1-marcandre.lureau@redhat.com> <20180215213312.29234-12-marcandre.lureau@redhat.com> <20180227020104-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 28, 2018 at 01:27:02PM +0100, Marc-André Lureau wrote: > Hi > > On Tue, Feb 27, 2018 at 1:04 AM, Michael S. Tsirkin wrote: > > On Thu, Feb 15, 2018 at 10:33:12PM +0100, Marc-André Lureau wrote: > >> Modify fw_cfg_read_blob() to use DMA if the device supports it. > >> Return errors, because the operation may fail. > >> > >> So far, only one call in fw_cfg_register_dir_entries() is using > >> kmalloc'ed buf and is thus clearly eligible to DMA read. > >> > >> Initially, I didn't implement DMA read to speed up boot time, but as a > >> first step before introducing DMA write (since read operations were > >> already presents). Even more, I didn't realize fw-cfg entries were > >> being read by the kernel during boot by default. But actally fw-cfg > >> entries are being populated during module probe. I knew DMA improved a > >> lot bios boot time (the main reason the DMA interface was added > >> afaik). Let see the time it would take to read the whole ACPI > >> tables (128kb allocated) > >> > >> # time cat /sys/firmware/qemu_fw_cfg/by_name/etc/acpi/tables/raw > >> - with DMA: sys 0m0.003s > >> - without DMA (-global fw_cfg.dma_enabled=off): sys 0m7.674s > >> > >> FW_CFG_FILE_DIR (0x19) is the only "file" that is read during kernel > >> boot to populate sysfs qemu_fw_cfg directory, and it is quite > >> small (1-2kb). Since it does not expose itself, in order to measure > >> the time it takes to read such small file, I took a comparable sized > >> file of 2048 bytes and exposed it (-fw_cfg test,file=file with a > >> modified read_raw enabling DMA) > >> > >> # perf stat -r 100 cat /sys/firmware/qemu_fw_cfg/by_name/test/raw >/dev/null > >> - with DMA: > >> 0.636037 task-clock (msec) # 0.141 CPUs utilized ( +- 1.19% ) > >> - without DMA: > >> 6.430128 task-clock (msec) # 0.622 CPUs utilized ( +- 0.22% ) > >> > >> That's a few msec saved during boot by enabling DMA read (the gain > >> would be more substantial if other & bigger fw-cfg entries are read by > >> others from sysfs, unfortunately, it's not clear if we can always > >> enable DMA there) > >> > >> Signed-off-by: Marc-André Lureau > >> --- > >> drivers/firmware/qemu_fw_cfg.c | 61 ++++++++++++++++++++++++++++++++++-------- > >> 1 file changed, 50 insertions(+), 11 deletions(-) > >> > >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c > >> index 3015e77aebca..94df57e9be66 100644 > >> --- a/drivers/firmware/qemu_fw_cfg.c > >> +++ b/drivers/firmware/qemu_fw_cfg.c > >> @@ -124,12 +124,47 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control) > >> return ret; > >> } > >> > >> +/* with acpi & dev locks taken */ > >> +static ssize_t fw_cfg_read_blob_dma(u16 key, > >> + void *buf, loff_t pos, size_t count) > >> +{ > >> + ssize_t ret; > >> + > >> + if (pos == 0) { > >> + ret = fw_cfg_dma_transfer(buf, count, key << 16 > >> + | FW_CFG_DMA_CTL_SELECT > >> + | FW_CFG_DMA_CTL_READ); > >> + } else { > >> + fw_cfg_sel_endianness(key); > >> + ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP); > >> + if (ret < 0) > >> + return ret; > >> + ret = fw_cfg_dma_transfer(buf, count, > >> + FW_CFG_DMA_CTL_READ); > >> + } > >> + > >> + return ret; > >> +} > >> + > >> +/* with acpi & dev locks taken */ > >> +static ssize_t fw_cfg_read_blob_io(u16 key, > >> + void *buf, loff_t pos, size_t count) > >> +{ > >> + fw_cfg_sel_endianness(key); > >> + while (pos-- > 0) > >> + ioread8(fw_cfg_reg_data); > >> + ioread8_rep(fw_cfg_reg_data, buf, count); > >> + return count; > >> +} > >> + > >> /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */ > >> static ssize_t fw_cfg_read_blob(u16 key, > >> - void *buf, loff_t pos, size_t count) > >> + void *buf, loff_t pos, size_t count, > >> + bool dma) > >> { > >> u32 glk = -1U; > >> acpi_status status; > >> + ssize_t ret; > >> > >> /* If we have ACPI, ensure mutual exclusion against any potential > >> * device access by the firmware, e.g. via AML methods: > > > > so this adds a dma flag to fw_cfg_read_blob. > > > > > > > >> @@ -143,14 +178,17 @@ static ssize_t fw_cfg_read_blob(u16 key, > >> } > >> > >> mutex_lock(&fw_cfg_dev_lock); > >> - fw_cfg_sel_endianness(key); > >> - while (pos-- > 0) > >> - ioread8(fw_cfg_reg_data); > >> - ioread8_rep(fw_cfg_reg_data, buf, count); > >> + if (dma && fw_cfg_dma_enabled()) { > >> + ret = fw_cfg_read_blob_dma(key, buf, pos, count); > >> + } else { > >> + ret = fw_cfg_read_blob_io(key, buf, pos, count); > >> + } > >> + > >> mutex_unlock(&fw_cfg_dev_lock); > >> > >> acpi_release_global_lock(glk); > >> - return count; > >> + > >> + return ret; > >> } > >> > >> #ifdef CONFIG_CRASH_CORE > > > > If set to false it does io, if set to true it does dma. > > > > I would prefer passing an accessor function pointer > > since that's clearer than true/false. > > ok > > > > >> @@ -284,7 +322,7 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev) > >> > >> /* verify fw_cfg device signature */ > >> if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, > >> - 0, FW_CFG_SIG_SIZE) < 0 || > >> + 0, FW_CFG_SIG_SIZE, false) < 0 || > >> memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { > >> fw_cfg_io_cleanup(); > >> return -ENODEV; > >> @@ -468,7 +506,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj, > >> if (count > entry->size - pos) > >> count = entry->size - pos; > >> > >> - return fw_cfg_read_blob(entry->select, buf, pos, count); > >> + /* do not use DMA, virt_to_phys(buf) might not be ok */ > >> + return fw_cfg_read_blob(entry->select, buf, pos, count, false); > >> } > >> > >> static struct bin_attribute fw_cfg_sysfs_attr_raw = { > >> @@ -634,7 +673,7 @@ static int fw_cfg_register_dir_entries(void) > >> size_t dir_size; > >> > >> ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files_count, > >> - 0, sizeof(files_count)); > >> + 0, sizeof(files_count), false); > >> if (ret < 0) > >> return ret; > >> > >> @@ -646,7 +685,7 @@ static int fw_cfg_register_dir_entries(void) > >> return -ENOMEM; > >> > >> ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, > >> - sizeof(files_count), dir_size); > >> + sizeof(files_count), dir_size, false); > >> if (ret < 0) > >> goto end; > >> > >> @@ -697,7 +736,7 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev) > >> goto err_probe; > >> > >> /* get revision number, add matching top-level attribute */ > >> - err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev)); > >> + err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), false); > >> if (err < 0) > >> goto err_probe; > > > > > > Looks like all callers pass in false as parameter. > > Given this, how can this speed up any operations? > > > > Are you sure you tested this properly? > > > I did modify read_raw to conduct testing ( the part "with a > modified read_raw enabling DMA" should be before, updating commit message). So this patch does nothing, it's just infrastructure so DMA can be enabled in the future - is that right? > > > >> -- > >> 2.16.1.73.g5832b7e9f2