From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752490AbeB1M1E convert rfc822-to-8bit (ORCPT ); Wed, 28 Feb 2018 07:27:04 -0500 Received: from mail-qt0-f195.google.com ([209.85.216.195]:38493 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752291AbeB1M1D (ORCPT ); Wed, 28 Feb 2018 07:27:03 -0500 X-Google-Smtp-Source: AG47ELtqmCyfVAnWtLFJFdiGgHSPSSu7DzL3omIlOvHewsULWPxDCwfxaBNwwaecY914hqZzkhZ6ierINzUPuIEKOuE= MIME-Version: 1.0 In-Reply-To: <20180227020104-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> From: =?UTF-8?B?TWFyYy1BbmRyw6kgTHVyZWF1?= Date: Wed, 28 Feb 2018 13:27:02 +0100 Message-ID: Subject: Re: [PATCH v15 11/11] RFC: fw_cfg: do DMA read operation To: "Michael S. Tsirkin" Cc: Linux Kernel Mailing List , Sergio Lopez Pascual , Baoquan He , "Somlo, Gabriel" , xiaolong.ye@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). > >> -- >> 2.16.1.73.g5832b7e9f2