Re: [PATCH v3 2/2] drm/xe/guc: Compress GuC log and CTB dump with zstd

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Jun 30, 2026 at 01:35:57PM -0400, Dong, Zhanjun wrote:
> Please see my inline comments below.
> 
> Regards,
> Zhanjun Dong
> 
> On 2026-06-30 12:32 a.m., Matthew Brost wrote:
> > On Mon, Jun 29, 2026 at 01:22:39PM -0400, Zhanjun Dong wrote:
> > > Replace the raw ascii85 dumps of GuC log snapshots with a
> > > zstd-compressed ascii85 stream and reuse the same helper for CTB
> > > snapshot output.
> > > 
> > > Use zstd streaming with default level-3 parameters and an estimated
> > > source size of 0 so the compression workspace stays bounded even for
> > > multi-megabyte logs.
> > > 
> > > Add a new Kconfig option DRM_XE_COMPRESS_DUMP to control whether
> > > GuC log and CTB dumps are compressed with ZSTD. This allows users to
> > > choose between reduced dump sizes or lower memory usage.
> > > 
> > 
> > What is the advantage of doing this the KMD vs. getting the dump and
> > compressing it in user space before sharing it?
> 1. Timing impact
> There are KMD runtime challenges about dump too many data:
> a. Skip unused data.
> Existing code dumps whole buffer, which also prints out area not used (Like
> lots of lines of "Z"). This patch only print valid range in buffer.
> b. Compessed size
> Test shown a typical 75% compression ratio about valid GuC log data.
> 
> Print out 10MB debug data in ascii85 take quiet a lot of time, especially
> when print out to dmesg. Too long print out might cause timing impact to

When do we printk to dmesg - we should never be doing that afiak or we
do, that should be removed as dmesg is not a mechanism for scalable
error logging.

> runtime, which is bad for debug purpose.

We always split the snap step from print step, so if a print takes a
little longer, I really don't see the issue. 

> With fewer data, this relifes KMD pressure when triggered.
> 
> 2. UMD utility required

cp /sys/class/drm/card0/device/devcoredump/data devcoredump.txt
gzip devcoredump.txt

?

> Do it in UMD requires an utility running in background and check/receive for
> data. If through debugfs, all above timing impact is not skipped.
> This add extra step for CI and user, in case of utility missing/offline, the
> valueable issue data would be lost
> 
> Meanwhile, there is discussion to have that kind of utility, will keep
> monitoring it.
> > 
> > > Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
> > > ---
> > >   drivers/gpu/drm/xe/Kconfig          |  16 +++
> > >   drivers/gpu/drm/xe/xe_devcoredump.c |   4 +-
> > >   drivers/gpu/drm/xe/xe_guc_ct.c      |  19 ++--
> > >   drivers/gpu/drm/xe/xe_guc_ct.h      |   4 +-
> > >   drivers/gpu/drm/xe/xe_guc_log.c     | 161 +++++++++++++++++++++++++---
> > >   drivers/gpu/drm/xe/xe_guc_log.h     |   9 +-
> > >   6 files changed, 184 insertions(+), 29 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/Kconfig b/drivers/gpu/drm/xe/Kconfig
> > > index 4d7dcaff2b91..3af15a0c14f7 100644
> > > --- a/drivers/gpu/drm/xe/Kconfig
> > > +++ b/drivers/gpu/drm/xe/Kconfig
> > > @@ -33,6 +33,8 @@ config DRM_XE
> > >   	select ACPI_WMI if X86 && ACPI
> > >   	select SYNC_FILE
> > >   	select CRC32
> > > +	select ZSTD_COMPRESS if DRM_XE_COMPRESS_DUMP
> > > +	select ZSTD_DECOMPRESS if DRM_XE_COMPRESS_DUMP
> > >   	select SND_HDA_I915 if SND_HDA_CORE
> > >   	select CEC_CORE if CEC_NOTIFIER
> > >   	select VMAP_PFN
> > > @@ -101,6 +103,20 @@ config DRM_XE_PAGEMAP
> > >   	  If in doubt say "Y".
> > > +config DRM_XE_COMPRESS_DUMP
> > > +	bool "Enable ZSTD compression for error dumps"
> > > +	depends on DRM_XE
> > > +	default y
> > 
> > Are tools to decode GuC logs updated to handle this mode?
> Current intel_dump_decode only support i915, we need more Xe debug support.>

That is not true. I have local repo with tools to decode GuC logs.

The answer must be yes, we have updated all internal tools, wikis before
we even considering merging this.
 
Matt

> > Matt
> > 
> > > +	help
> > > +	  Enable this option to compress GuC log and CTB dumps with ZSTD
> > > +	  compression. This can significantly reduce the size of error dumps
> > > +	  but requires additional memory for compression workspace.
> > > +
> > > +	  Disable this option if you want to save memory or prefer uncompressed
> > > +	  error dumps for debugging.
> > > +
> > > +	  If in doubt say "Y".
> > > +
> > >   config DRM_XE_FORCE_PROBE
> > >   	string "Force probe xe for selected Intel hardware IDs"
> > >   	depends on DRM_XE
> > > diff --git a/drivers/gpu/drm/xe/xe_devcoredump.c b/drivers/gpu/drm/xe/xe_devcoredump.c
> > > index 5f2b90b18f97..27473c25aad2 100644
> > > --- a/drivers/gpu/drm/xe/xe_devcoredump.c
> > > +++ b/drivers/gpu/drm/xe/xe_devcoredump.c
> > > @@ -115,9 +115,9 @@ static ssize_t __xe_devcoredump_read(char *buffer, ssize_t count,
> > >   	drm_printf(&p, "\tTile: %d\n", ss->gt->tile->id);
> > >   	drm_puts(&p, "\n**** GuC Log ****\n");
> > > -	xe_guc_log_snapshot_print(ss->guc.log, &p);
> > > +	xe_guc_log_snapshot_print(ss->guc.log, &p, ss->gt);
> > >   	drm_puts(&p, "\n**** GuC CT ****\n");
> > > -	xe_guc_ct_snapshot_print(ss->guc.ct, &p);
> > > +	xe_guc_ct_snapshot_print(ss->guc.ct, &p, ss->gt);
> > >   	drm_puts(&p, "\n**** Contexts ****\n");
> > >   	xe_guc_exec_queue_snapshot_print(ss->ge, &p);
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > index 21e0dad9a481..4cedbcdb831e 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > @@ -2094,11 +2094,12 @@ struct xe_guc_ct_snapshot *xe_guc_ct_snapshot_capture(struct xe_guc_ct *ct)
> > >    * xe_guc_ct_snapshot_print - Print out a given GuC CT snapshot.
> > >    * @snapshot: GuC CT snapshot object.
> > >    * @p: drm_printer where it will be printed out.
> > > + * @gt: GT structure for error reporting
> > >    *
> > >    * This function prints out a given GuC CT snapshot object.
> > >    */
> > >   void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot,
> > > -			      struct drm_printer *p)
> > > +			      struct drm_printer *p, struct xe_gt *gt)
> > >   {
> > >   	if (!snapshot)
> > >   		return;
> > > @@ -2112,11 +2113,10 @@ void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot,
> > >   		drm_printf(p, "\tg2h outstanding: %d\n",
> > >   			   snapshot->g2h_outstanding);
> > > -		if (snapshot->ctb) {
> > > -			drm_printf(p, "[CTB].length: 0x%zx\n", snapshot->ctb_size);
> > > -			xe_print_blob_ascii85(p, "[CTB].data", '\n',
> > > -					      snapshot->ctb, 0, snapshot->ctb_size);
> > > -		}
> > > +		if (snapshot->ctb)
> > > +			xe_guc_print_blob(gt, p, "[CTB]", "[CTB].data",
> > > +					  &snapshot->ctb, 1,
> > > +					  snapshot->ctb_size, snapshot->ctb_size);
> > >   	} else {
> > >   		drm_puts(p, "CT disabled\n");
> > >   	}
> > > @@ -2150,9 +2150,10 @@ void xe_guc_ct_snapshot_free(struct xe_guc_ct_snapshot *snapshot)
> > >   void xe_guc_ct_print(struct xe_guc_ct *ct, struct drm_printer *p, bool want_ctb)
> > >   {
> > >   	struct xe_guc_ct_snapshot *snapshot;
> > > +	struct xe_gt *gt = ct_to_gt(ct);
> > >   	snapshot = guc_ct_snapshot_capture(ct, false, want_ctb);
> > > -	xe_guc_ct_snapshot_print(snapshot, p);
> > > +	xe_guc_ct_snapshot_print(snapshot, p, gt);
> > >   	xe_guc_ct_snapshot_free(snapshot);
> > >   }
> > > @@ -2250,10 +2251,10 @@ static void ct_dead_print(struct xe_dead_ct *dead)
> > >   	drm_printf(&lp, "\tTile: %d\n", gt->tile->id);
> > >   	drm_puts(&lp, "**** GuC Log ****\n");
> > > -	xe_guc_log_snapshot_print(dead->snapshot_log, &lp);
> > > +	xe_guc_log_snapshot_print(dead->snapshot_log, &lp, gt);
> > >   	drm_puts(&lp, "**** GuC CT ****\n");
> > > -	xe_guc_ct_snapshot_print(dead->snapshot_ct, &lp);
> > > +	xe_guc_ct_snapshot_print(dead->snapshot_ct, &lp, gt);
> > >   	drm_puts(&lp, "Done.\n");
> > >   }
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.h b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > index 767365a33dee..2005d1a0cd6c 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_ct.h
> > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > @@ -10,6 +10,7 @@
> > >   struct drm_printer;
> > >   struct xe_device;
> > > +struct xe_gt;
> > >   int xe_guc_ct_init_noalloc(struct xe_guc_ct *ct);
> > >   int xe_guc_ct_init(struct xe_guc_ct *ct);
> > > @@ -24,7 +25,8 @@ void xe_guc_ct_flush_and_stop(struct xe_guc_ct *ct);
> > >   void xe_guc_ct_fast_path(struct xe_guc_ct *ct);
> > >   struct xe_guc_ct_snapshot *xe_guc_ct_snapshot_capture(struct xe_guc_ct *ct);
> > > -void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot, struct drm_printer *p);
> > > +void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot, struct drm_printer *p,
> > > +			      struct xe_gt *gt);
> > >   void xe_guc_ct_snapshot_free(struct xe_guc_ct_snapshot *snapshot);
> > >   void xe_guc_ct_print(struct xe_guc_ct *ct, struct drm_printer *p, bool want_ctb);
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_log.c b/drivers/gpu/drm/xe/xe_guc_log.c
> > > index 538d4df0f7aa..d20be1a064f1 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_log.c
> > > +++ b/drivers/gpu/drm/xe/xe_guc_log.c
> > > @@ -6,6 +6,9 @@
> > >   #include "xe_guc_log.h"
> > >   #include <linux/fault-inject.h>
> > > +#if IS_ENABLED(CONFIG_DRM_XE_COMPRESS_DUMP)
> > > +#include <linux/zstd.h>
> > > +#endif
> > >   #include <linux/utsname.h>
> > >   #include <drm/drm_managed.h>
> > > @@ -225,16 +228,148 @@ struct xe_guc_log_snapshot *xe_guc_log_snapshot_capture(struct xe_guc_log *log,
> > >   	return snapshot;
> > >   }
> > > +#if IS_ENABLED(CONFIG_DRM_XE_COMPRESS_DUMP)
> > > +static void xe_guc_print_blob_compressed(struct xe_gt *gt, struct drm_printer *p,
> > > +					 const char *length_label, const char *data_label,
> > > +					 void **chunks, int num_chunks,
> > > +					 size_t chunk_size, size_t total_size)
> > > +{
> > > +	zstd_parameters params;
> > > +	zstd_cstream *cstream;
> > > +	zstd_out_buffer outbuf;
> > > +	size_t wksp_size, dst_size;
> > > +	size_t remain, ret;
> > > +	void *wksp = NULL;
> > > +	char *dst = NULL;
> > > +	int i;
> > > +
> > > +	/*
> > > +	 * Pass 0 as estimated_src_size to use zstd level-3 defaults
> > > +	 * (windowLog=18, 256KB window). Passing the full total_size would
> > > +	 * cause zstd to inflate windowLog proportionally (e.g. windowLog=24
> > > +	 * for a 19MB log), making the workspace tens of MB.  With 0, the
> > > +	 * workspace stays ~1.5MB, well within kmalloc limits.
> > > +	 */
> > > +	params = zstd_get_params(3, 0);
> > > +
> > > +	wksp_size = zstd_cstream_workspace_bound(&params.cParams);
> > > +	wksp = kvzalloc(wksp_size, GFP_KERNEL);
> > > +	if (!wksp)
> > > +		goto err;
> > > +
> > > +	dst_size = zstd_compress_bound(total_size);
> > > +	dst = kvzalloc(dst_size, GFP_KERNEL);
> > > +	if (!dst)
> > > +		goto err;
> > > +
> > > +	cstream = zstd_init_cstream(&params, 0, wksp, wksp_size);
> > > +	if (!cstream) {
> > > +		xe_gt_err(gt, "failed to init zstd cstream\n");
> > > +		goto err;
> > > +	}
> > > +
> > > +	outbuf.dst = dst;
> > > +	outbuf.size = dst_size;
> > > +	outbuf.pos = 0;
> > > +
> > > +	remain = total_size;
> > > +	for (i = 0; i < num_chunks && remain; i++) {
> > > +		size_t size = min(chunk_size, remain);
> > > +		zstd_in_buffer inbuf = { .src = chunks[i], .size = size, .pos = 0 };
> > > +
> > > +		while (inbuf.pos < inbuf.size) {
> > > +			ret = zstd_compress_stream(cstream, &outbuf, &inbuf);
> > > +			if (zstd_is_error(ret)) {
> > > +				xe_gt_err(gt, "zstd_compress_stream failed: %s\n",
> > > +					  zstd_get_error_name(ret));
> > > +				goto err;
> > > +			}
> > > +		}
> > > +		remain -= size;
> > > +	}
> > > +
> > > +	do {
> > > +		ret = zstd_end_stream(cstream, &outbuf);
> > > +		if (zstd_is_error(ret)) {
> > > +			xe_gt_err(gt, "zstd_end_stream failed: %s\n",
> > > +				  zstd_get_error_name(ret));
> > > +			goto err;
> > > +		}
> > > +	} while (ret > 0 && outbuf.pos < outbuf.size);
> > > +
> > > +	drm_printf(p, "%s.length: 0x%zx -> 0x%zx Algo: ZSTD\n",
> > > +		   length_label, total_size, outbuf.pos);
> > > +	xe_print_blob_ascii85(p, data_label, '\n', dst, 0,
> > > +			      DIV_ROUND_UP(outbuf.pos, sizeof(u32)) * sizeof(u32));
> > > +	goto out;
> > > +
> > > +err:
> > > +	drm_printf(p, "%s.length: 0x%zx Algo: ERROR (compression failed)\n",
> > > +		   length_label, total_size);
> > > +out:
> > > +	kvfree(dst);
> > > +	kvfree(wksp);
> > > +}
> > > +#endif
> > > +
> > >   /**
> > > - * xe_guc_log_snapshot_print - dump a previously saved copy of the GuC log to some useful location
> > > - * @snapshot: a snapshot of the GuC log
> > > - * @p: the printer object to output to
> > > + * xe_guc_print_blob - Print binary data (compressed or uncompressed) as ascii85
> > > + * @gt: GT structure for error reporting
> > > + * @p: drm_printer for output
> > > + * @length_label: label prefix for the length/metadata line (e.g. "[LOG]" or "[CTB]")
> > > + * @data_label: label for the ascii85 blob (e.g. "[LOG].data" or "[CTB].data")
> > > + * @chunks: array of pointers to source data chunks
> > > + * @num_chunks: number of elements in @chunks
> > > + * @chunk_size: nominal size of each chunk; the last chunk may hold fewer valid bytes
> > > + * @total_size: total uncompressed byte count across all chunks
> > > + *
> > > + * If CONFIG_DRM_XE_COMPRESS_DUMP is enabled, compresses @total_size bytes using
> > > + * zstd level-3 streaming compression and prints the result via @p using ascii85
> > > + * encoding. Otherwise, directly prints the uncompressed data.
> > > + * On failure the function returns without printing the data blob.
> > >    */
> > > -void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_printer *p)
> > > +void xe_guc_print_blob(struct xe_gt *gt __maybe_unused, struct drm_printer *p,
> > > +		       const char *length_label, const char *data_label,
> > > +		       void **chunks, int num_chunks,
> > > +		       size_t chunk_size, size_t total_size)
> > >   {
> > > +#if IS_ENABLED(CONFIG_DRM_XE_COMPRESS_DUMP)
> > > +	xe_guc_print_blob_compressed(gt, p, length_label, data_label,
> > > +				     chunks, num_chunks, chunk_size, total_size);
> > > +#else
> > > +	/* Compression disabled, output uncompressed data directly */
> > >   	size_t remain;
> > >   	int i;
> > > +	drm_printf(p, "%s.length: 0x%zx Algo: RAW\n", length_label, total_size);
> > > +
> > > +	/*
> > > +	 * Print each chunk directly without merging into a single buffer.
> > > +	 * xe_print_blob_ascii85() supports multiple calls - use suffix=0
> > > +	 * for all but the last chunk to omit the newline between chunks.
> > > +	 */
> > > +	remain = total_size;
> > > +	for (i = 0; i < num_chunks && remain; i++) {
> > > +		size_t size = min(chunk_size, remain);
> > > +		const char *prefix = i ? NULL : data_label;
> > > +		/* Add suffix only on the last chunk */
> > > +		char suffix = (remain == size) ? '\n' : 0;
> > > +
> > > +		xe_print_blob_ascii85(p, prefix, suffix, chunks[i], 0,
> > > +				      DIV_ROUND_UP(size, sizeof(u32)) * sizeof(u32));
> > > +		remain -= size;
> > > +	}
> > > +#endif
> > > +}
> > > +
> > > +/**
> > > + * xe_guc_log_snapshot_print - dump a previously saved copy of the GuC log to some useful location
> > > + * @snapshot: a snapshot of the GuC log
> > > + * @p: the printer object to output to
> > > + */
> > > +void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_printer *p,
> > > +			       struct xe_gt *gt)
> > > +{
> > >   	if (!snapshot) {
> > >   		drm_printf(p, "GuC log snapshot not allocated!\n");
> > >   		return;
> > > @@ -248,16 +383,9 @@ void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_
> > >   	drm_printf(p, "GuC timestamp: 0x%08llX [%llu]\n", snapshot->stamp, snapshot->stamp);
> > >   	drm_printf(p, "Log level: %u\n", snapshot->level);
> > > -	drm_printf(p, "[LOG].length: 0x%zx\n", snapshot->size);
> > > -	remain = snapshot->size;
> > > -	for (i = 0; i < snapshot->num_chunks; i++) {
> > > -		size_t size = min(GUC_LOG_CHUNK_SIZE, remain);
> > > -		const char *prefix = i ? NULL : "[LOG].data";
> > > -		char suffix = i == snapshot->num_chunks - 1 ? '\n' : 0;
> > > -
> > > -		xe_print_blob_ascii85(p, prefix, suffix, snapshot->copy[i], 0, size);
> > > -		remain -= size;
> > > -	}
> > > +	xe_guc_print_blob(gt, p, "[LOG]", "[LOG].data",
> > > +			  snapshot->copy, snapshot->num_chunks,
> > > +			  GUC_LOG_CHUNK_SIZE, snapshot->size);
> > >   }
> > >   static inline void lfd_output_binary(struct drm_printer *p, char *buf, int buf_size)
> > > @@ -598,12 +726,13 @@ void xe_guc_log_print_dmesg(struct xe_guc_log *log)
> > >   void xe_guc_log_print(struct xe_guc_log *log, struct drm_printer *p)
> > >   {
> > >   	struct xe_guc_log_snapshot *snapshot;
> > > +	struct xe_gt *gt = log_to_gt(log);
> > >   	drm_printf(p, "**** GuC Log ****\n");
> > >   	snapshot = xe_guc_log_snapshot_capture(log, false);
> > > -	drm_printf(p, "CS reference clock: %u\n", log_to_gt(log)->info.reference_clock);
> > > -	xe_guc_log_snapshot_print(snapshot, p);
> > > +	drm_printf(p, "CS reference clock: %u\n", gt->info.reference_clock);
> > > +	xe_guc_log_snapshot_print(snapshot, p, gt);
> > >   	xe_guc_log_snapshot_free(snapshot);
> > >   }
> > > diff --git a/drivers/gpu/drm/xe/xe_guc_log.h b/drivers/gpu/drm/xe/xe_guc_log.h
> > > index 4649a260755e..3e97647ee8b5 100644
> > > --- a/drivers/gpu/drm/xe/xe_guc_log.h
> > > +++ b/drivers/gpu/drm/xe/xe_guc_log.h
> > > @@ -11,6 +11,7 @@
> > >   struct drm_printer;
> > >   struct xe_device;
> > > +struct xe_gt;
> > >   #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_GUC)
> > >   #define XE_GUC_LOG_EVENT_DATA_BUFFER_SIZE	SZ_16M
> > > @@ -59,7 +60,13 @@ void xe_guc_log_print(struct xe_guc_log *log, struct drm_printer *p);
> > >   void xe_guc_log_print_lfd(struct xe_guc_log *log, struct drm_printer *p);
> > >   void xe_guc_log_print_dmesg(struct xe_guc_log *log);
> > >   struct xe_guc_log_snapshot *xe_guc_log_snapshot_capture(struct xe_guc_log *log, bool atomic);
> > > -void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_printer *p);
> > > +
> > > +void xe_guc_print_blob(struct xe_gt *gt, struct drm_printer *p, const char *length_label,
> > > +		       const char *data_label, void **chunks, int num_chunks,
> > > +		       size_t chunk_size, size_t total_size);
> > > +
> > > +void xe_guc_log_snapshot_print(struct xe_guc_log_snapshot *snapshot, struct drm_printer *p,
> > > +			       struct xe_gt *gt);
> > >   void xe_guc_log_snapshot_free(struct xe_guc_log_snapshot *snapshot);
> > >   static inline u32
> > > -- 
> > > 2.34.1
> > > 
>