@@ -141,6 +141,7 @@ sd_store_cache_type(struct device *dev, struct device_attribute *attr,
char *buffer_data;
struct scsi_mode_data data;
struct scsi_sense_hdr sshdr;
+ const char *temp = "temporary ";
int len;
if (sdp->type != TYPE_DISK)
@@ -149,6 +150,13 @@ sd_store_cache_type(struct device *dev, struct device_attribute *attr,
* it's not worth the risk */
return -EINVAL;
+ if (strncmp(buf, temp, sizeof(temp) - 1) == 0) {
+ buf += sizeof(temp) - 1;
+ sdkp->cache_override = 1;
+ } else {
+ sdkp->cache_override = 0;
+ }
+
for (i = 0; i < ARRAY_SIZE(sd_cache_types); i++) {
len = strlen(sd_cache_types[i]);
if (strncmp(sd_cache_types[i], buf, len) == 0 &&
@@ -161,6 +169,13 @@ sd_store_cache_type(struct device *dev, struct device_attribute *attr,
return -EINVAL;
rcd = ct & 0x01 ? 1 : 0;
wce = ct & 0x02 ? 1 : 0;
+
+ if (sdkp->cache_override) {
+ sdkp->WCE = wce;
+ sdkp->RCD = rcd;
+ return count;
+ }
+
if (scsi_mode_sense(sdp, 0x08, 8, buffer, sizeof(buffer), SD_TIMEOUT,
SD_MAX_RETRIES, &data, NULL))
return -EINVAL;
@@ -2127,6 +2142,10 @@ sd_read_cache_type(struct scsi_disk *sdkp, unsigned char *buffer)
int old_rcd = sdkp->RCD;
int old_dpofua = sdkp->DPOFUA;
+
+ if (sdkp->cache_override)
+ return;
+
first_len = 4;
if (sdp->skip_ms_page_8) {
if (sdp->type == TYPE_RBC)
@@ -2608,6 +2627,7 @@ static void sd_probe_async(void *data, async_cookie_t cookie)
sdkp->capacity = 0;
sdkp->media_present = 1;
sdkp->write_prot = 0;
+ sdkp->cache_override = 0;
sdkp->WCE = 0;
sdkp->RCD = 0;
sdkp->ATO = 0;
@@ -67,6 +67,7 @@ struct scsi_disk {
u8 protection_type;/* Data Integrity Field */
u8 provisioning_mode;
unsigned ATO : 1; /* state of disk ATO bit */
+ unsigned cache_override : 1; /* temp override of WCE,RCD */
unsigned WCE : 1; /* state of disk WCE bit */
unsigned RCD : 1; /* state of disk RCD bit, unused */
unsigned DPOFUA : 1; /* state of disk DPOFUA bit */
This is a note to let you know that I have just added a patch titled sd: fix array cache flushing bug causing performance problems to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From e65f69107016384c7ba7bf7380ac3079c87240ff Mon Sep 17 00:00:00 2001 From: James Bottomley <JBottomley@Parallels.com> Date: Wed, 24 Apr 2013 14:02:53 -0700 Subject: [PATCH] sd: fix array cache flushing bug causing performance problems commit 39c60a0948cc06139e2fbfe084f83cb7e7deae3b upstream. Some arrays synchronize their full non volatile cache when the sd driver sends a SYNCHRONIZE CACHE command. Unfortunately, they can have Terrabytes of this and we send a SYNCHRONIZE CACHE for every barrier if an array reports it has a writeback cache. This leads to massive slowdowns on journalled filesystems. The fix is to allow userspace to turn off the writeback cache setting as a temporary measure (i.e. without doing the MODE SELECT to write it back to the device), so even though the device reported it has a writeback cache, the user, knowing that the cache is non volatile and all they care about is filesystem correctness, can turn that bit off in the kernel and avoid the performance ruinous (and safety irrelevant) SYNCHRONIZE CACHE commands. The way you do this is add a 'temporary' prefix when performing the usual cache setting operations, so echo temporary write through > /sys/class/scsi_disk/<disk>/cache_type Reported-by: Ric Wheeler <rwheeler@redhat.com> Signed-off-by: James Bottomley <JBottomley@Parallels.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/scsi/sd.c | 20 ++++++++++++++++++++ drivers/scsi/sd.h | 1 + 2 files changed, 21 insertions(+) -- 1.8.1.2